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PREFACE 

TO THE FIRST EDITION. 


The collection of papers which forms this book was mostly 
prepared in moments stolen from more active professional duties, 
and must consequently lack the uniformity and completeness 
which is compatible only with ample leisure and freedom from 
other more pressing- cares. 

It has been my intention to confine myself principally to 
facts gleaned from my own experience, and only to touch upon 
theoretical questions when essential for the understanding of 
practical facts. 

As the items of cost, both of construction and subsequent 
operation, are amongst the most important of all the practical 
questions that face the originators of new smelting enterprises, 
and as these are virtually unattainable to the general public, I 
have gone into these figures in considerable detail, not calculating 
expenses as they appear on paper, and when everything is run¬ 
ning smoothly, but giving the actual results of building on a 
large scale, and of smelting many thousand tons of ores under 
varying circumstances, and in all of the ordinary kinds of fur¬ 
naces. 

Owing to the magnitude of the subject, I found it impossible to 
touch upon the so-called “Wet Methods” without increasing the 
size and consequent cost of this volume to an extent that might 
probably peril its circulation. 

The author desires to acknowledge the valuable assistance of 
Mr. J. E. Mills, in connection with the geology of the Butte min¬ 
ing district, and to credit Mr. H. M. Howe and Mr. A. F. Wendt 
with the use he has made of their papers on “Copper Smelting” 
and on “ The Pyrites Deposits of the Alleglianies.” 

But, above all, he has to thank Mr. James Douglas for a thor¬ 
ough and minute revision and criticism of his manuscript just 
before publication. 

E. D. P., Jr. 

Walpole, Mass., June, 1887. 


to~ /%S 07 




PREFACE 


TO THE SECOND EDITION. 


The time which has elapsed since the exhaustion of the large 
first edition of this book has given an opportunity for its thor¬ 
ough revision, as well as for the addition of such new material as 
time and experience have suggested. The advances in copper 
smelting since this work first appeared have been rather in a 
general enlargement of furnaces and apparatus than in any 
radical changes or inventions. 

Amongst many friends who have given their valuable assist¬ 
ance I desire to mention, in particular, Mr. Francis L. Sperry, 
of Sudbury, Ontario, for five years analytical chemist for the 
Canadian Copper Co., who has prepared the section on the 
Electrolytic Assay of Copper, and Mr. Paul Johnson, of Sweden, 
who has furnished me valuable information and plans of the 
regenerative gas furnaces for copper refining now used at Atvid- 
aberg. Sweden. I have ventured to introduce this description of 
foreign practice in the belief that it is to the use of regenerative 
gas furnaces that we must look for any great economy in fuel, a 
point absolutely vital in some of our Western mining districts. 

E. D. P., Jr. 

New York, November, 1891. 



PREFACE 


TO THE THIRD EDITION. 


It is scarcely a month since I appended my initials to the 
Preface to the Second Edition of this book. 

The sheets of that edition had barely time to lose the moisture 
from the operation of printing before they were exhausted. 

Consequently I have no changes to make in the text, and 
nothing to offer as a preface, except my sincere thanks to the 
Public at Large, and to my Brother-Metallurgists in particular, 
for the extreme kindness with which they have received this rec- 
ord of personal experience. 

Amongst some thirty or forty elaborate reviews and criticisms 
of this work, published in magazines and journals scattered all 
over the world, I have not seen a single word of fault-finding • 
while I have felt almost overwhelmed by the unanimous praise 
that they have independently bestowed upon it. 

It is an ample reward for the great labor and time that must 
be expended by whomever undertakes to write a technical book. 

E. D. P., Jr. 

Boston, December, 1891. 





CONTENTS. 


PAGE 

PREFACE. 

CHAPTER I.— Description of the Ores of Copper . 1-6 

Native Copper, Cuprite, 1. Melaconite, 2. Malachite, Azurite, 
Chalcopyrite, 3. Ckalcocite, 4. Bornite, Tetrahedrite, 5. 

CHAPTER II.— Distribution of the Ores of Copper . 7-28 

Division into Four Districts, 7. Atlantic Coast Beds, 7. Lake 
Deposits, 9. Calumet & Hecla, Tamarack, 12. Mountain Sys¬ 
tem of Veins, 15. Butte City Mines, 16. Colorado Mines, 17. 
Southern Carbonate Deposits, 18. Arizona Mines, 20. The 
Future of Copper in the U. S., 22. No Danger of Excessive 
Production, 24-28. 

CHAPTER III.— Methods of Copper Assaying . 29-44 

Sampling, 29. Brunton’s Automatic Sampler, 30. Brunton’s 
Quartering Shovel, 32. Determination of Moisture, 32. Methods 
of Assaying, 33. Titration with KCy, 33. Substances that, in¬ 
validate the Cyanide Assay, 34. Table Showing Effect of Fe 2 Os 
on Cyanide Assay, 35. Torrey & Eaton’s Investigations on 
Cyanide Assay, 36. Precipitation with Zinc, 37. Colorimetric 
Determination of Copper, 37. The Electrolytic Method, 38. F. 

L. Sperry’s Description of “ The Determination of Copper by 
Electrolysis,” 39. Electrolytic Determination of Nickel, 43. 

CHAPTER IV.— The Roasting of Copper Ores in Lump Form. 45-91 

Varieties of Roasting, 46. Breaking of Ore for Roasting, 47. 
Comparative Production of Fines in Crushing Ores, 48. Classi¬ 
fication of Crushed Ore for Heap-roasting, 49. Arrangement of 
Crushing-plant for Heap-roasting, 50. Expense of Crushing 
Ore, 50. Breaking of Ore by Hand, 52. Cost of Breaking Ore 
by Hand, 55. Heap-roasting of Ore, 56. Injurious Effects of 
Heap-roasting, 57. Means for Obviating the Same, 58. Reme¬ 
dies for the Heap-roasting Nuisance at Butte City, 60. Prepa- 






Vlll 


CONTENTS. 


PA6E 

ration of Roast-yard, 61. Elevated Railroad over Roast-heaps, 

64. Table Showing Time Required to Roast Heaps of Various 
Sizes, 68. Building of Roast-lieaps, 69. Kindling Roast-heaps, 

72. Management of Roast-heaps, 73. Stripping Roast-heaps, 

78. Formation of Matte in Roast-heaps, 79. Percentage of Ore 
Well Roasted, 80. Removal of Roast-heap to Furnace, 81. Cost 
of Heap-roasting, 83. Degree of Desulphurization Attained, 84. 
Appearance of Roasted Ore, 86. The “ V-Method ” of Roasting, 

87. Heap-roasting of Matte, 88. Cost of Same, 91. 

CHAPTER V.— Stall-roasting . 92-117 

Open Stalls, 92. Manufacture of Slag-brick, 93. Roast Stalls 
for Ore, 96. Size of Chimney Required, 100. Fuel Required, 

101. Length of Operation, 103. Results of Stall-roasting, 105. 

Loss of Copper by Roasting in Open Air, 107. Cost of Stall- 
roasting, 109. Cost of Roast-stalls, 110. Stall-roasting of 
Matte, 115. Matte-stalls, 116. 

CHAPTER VI.— The Roasting of Ores in Lump Form in Kilns. 118-122 

Pyrites used in making Sulphuric Acid, 118. Mistaken L T se of 
Pyrrhotite, 120. Kilns for Acid-making, 121. 

CHAPTER VII.— Calcination of Ore and Matte in a Finely- 

divided Condition .123-167 

Granulation of Matte by Water, 125. Crushing Machinery, 126. 
Machines for Preparatory Crushing, 126. Machines for Final 
Pulverization, 128. Capacity of Crushing Plant, 133. Calcining 
Furnaces, 133. Shaft-furnaces for Calcining, 133. Revolving 
Cylinder Calciners, 135. Automatic Hearth Furnaces, 141. 

With Stationary Hearth. 141. With Movable Hearth, 146. 
Reverberatory Calciners, 146. With Open Hearth, 146. Con¬ 
struction of Calciners, 150. Construction of Furnace Stacks, 

159. Cost of Constructing Calcining-furnace, 165. 

CHAPTER VIII.— The Chemistry of the Calcining Process _168 -180 

“ Matte Fusion ” Assay, 174. Matte Production from Calcined 
Ore, 175. Cost of Calcining, 179. 

CHAPTER IX.— The Smelting of Copper .181-225 

Blast-furnace Smelting, Treatment of Sulphide Ores, 184. The 
Water-jacket Furnace, 186. Herreshoff’s Furnace, 195. Wendt’s 
Description of Herreshoff’s Furnace, 200. Smelters Running on 
Oxidized Ores, 210. The Management of Water-jacket Fur¬ 
naces, 211. Lake Superior Slag-cupola, 216. Comparative 
Results in Water-jackets, 220. 





CONTENTS. 


IX 


PAGE 

CHAPTER X. —Blast-furnaces Constructed of Brick .226-255 

Description of the Orford Furnace, 227. Construction of its 
Bottom, 232. Use of Silica in Over-hot Furnaces, 239. Allow¬ 
ing Furnaces to stand quiet over night, 243. Repairing Brick 
Furnaces, 248. Estimate of Cost of Brick Furnaces, 251. Esti¬ 
mate of Costs of Cupola-smelting, 253. 

CHAPTER XI. —General Remarks on Blast-furnace Smelting. 256-285 

Effect of Blast-pressure on Capacity of Furnace, 257. Size of 
Charge, 259. Blowers and Accessory Blast-apparatus, 265. 

Modern Accessory Blast-furnace Apparatus, 269. Matte-smelt¬ 
ing in Blast-furnaces, 271. Treatment of fine Ore in Blast-fur¬ 
naces, 275. Reduction of Furnace Capacity by Substitution of 
Ore Fines, 281. Results of Smelting Green Fines at Orford 
Co.’s Works, 284. Resume of Results of Cupola-smelting, 285. 

CHAPTER XII. —Late Improvements in Blast-furnaces .286-289 

Herreshoffs Improvements, 286. Use of Wrought-iron Furnace- 
wells, 287. The Granulation of Slag, 288. The Resulphuriza- 
tion of Metallic Copper, 289. 

CHAPTER XIII. —The Smelting of Pyritous Ores, Containing 

Copper and Nickel .290-298 

Occurrence of Nickeliferous Pyrrhotite in Ontario, 290. The 
Roasting of the Pyrrhotite, 291. Smelting of Nickel Ores, 294. 
Treatment of the Nickel Matte, 295. Fusion of Metallic Nickel 
in Quantity, 297. 


CHAPTER XIV.— Reverberatory Furnaces .299-362 

The Various Processes Executed in Reverberatories, 299. Details 
of Building a Reverberatory, 300. Drying New Furnace, 305. 
Material for Hearth, 306. Management of Furnace, 309. Re¬ 
sults of Reverberatory Smelting, 312. Estimate of Labor and 
Materials in Building Reverberatory, 312. Tools Required for 
Reverberatory, 316. Cost of Hearth-Bottoms, 317. Cost of 
Running Reverberatory Smelter per 24 hours, 318. Ore Smelt¬ 
ing for Coarse Metal, 319. Assays of Parrot Matte Shipments, 

• 320. Improvements in Reverberatory Smelting, 324. Argo Fur¬ 
naces, 326. Estimate of Material and Labor on New, Large 
Reverberatories, 331. Smelting for White Metal, 333. Table 
of Results of Matte Concentration by Oxidizing Fusion, 335. 

The Making of Blister Copper, 335. Gilchrist’s Basic-lined Fur¬ 
naces, 339. Table of Results of Treatment of Metallic Bottoms, 

341. Treatment of White or Pimple Metal on the Basic Hearth, 

342. Copper Refining, 343. Cost of Refining Copper, 360. 






x CONTENTS. 

PAGE 

CHAPTER XV.— Refining Copper with Gas in Sweden .363-377 

The Atvidaberg Regenerative Gas Plant for Copper Refining, 

363. The Blister Process at Atvidaberg, 364. The Refining of 
the Blister Copper in Gas-furnaces, 370. The Use of Basic-lined 
Furnaces for Refining Copper, 374. The Sacrifice of Lake Cop¬ 
per, 376. 

CHAPTER XVI.— Treatment of Gold- and Silver-bearing Cop¬ 
per Ores .378-379 

Concentration of Gold in Metallic Bottoms, 378. Saturation of 
Furnace Bottoms with the Precious Metals, 379. 

CHAPTER XVII.— The Bessemerizing of Copper Mattes .380-383 

Manhes Plant at the Parrot Works, 380. Description of Con¬ 
verter, 381. Difficulties Encountered and Vanquished, 381. 

Position of Tuyeres in the Manhes Converter, 381. Lining of 
Converter, 382. Saving of Cost by Converter, 382. Capacity of 
Converter, 383. Loss of Silver by A T olatilization, 383. Ca¬ 
pacity of the Parrot Bessemerizing Plant, 383. 





Modern American Methods 


OF 


Copper Smelting. 


chapter i. 

DESCRIPTION OF THE ORES OF COPPER. 

Although the copper-bearing minerals are numerous, yet 
those of commercial importance are few in number, and for the 
most part quite simple in chemical composition. The following 
minerals may be properly considered ores of copper, and are 
found in the United States in the localities enumerated. 

Native Metallic Copper, 

Aside from the extensive occurrence of this metal in the Lake 
Superior region and at Santa Rita, New Mexico, it is found very 
frequently as a product of decomposition, though seldom in 
sufficient quantities to render it of any commercial importance. 
It is usually remarkable for its purity. 

Cuprite, or Red Oxide of Copper, Cu 2 0; 88*8 Cu, 112 O. 

This mineral occurs solely as a product of decomposition, and 
while quite widely distributed, is nowhere an ore of any impor¬ 
tance, except in the Southwestern carbonate mines, where it some¬ 
times permeates large masses of iron oxide, notably increasing 
their copper contents. Quite large lumps of this mineral are 
found in the Santa Rita mines, and are evidently the result of an 
1 



2 MODERN AMERICAN METHODS OF COPPER SMELTING. 

oxidation of nodules of metallic copper, the unaltered center be¬ 
ing usually preserved of greater or less size.* Many of the Butte 
City veins, as well as fissures throughout the Eastern Coast 
Range, carry this mineral in their upper portions as a product 
of the decomposition of sulphide ores. 

Melaconite, Black Oxide of Copper, Cu 0 2 ; 79’8 Cu, 

20-2 O. 

This ore, with its metallic contents usually in part replaced by 
oxides of iron and manganese, is not quite so widely distributed 
as the sub-oxide, but is more frequently found in masses suffi¬ 
ciently large to pay for extraction. Its most remarkable occurrence 
in the United States was in the Blue Ridge mines of Tennessee, 
North Carolina, and Virginia, where the upper portion of the 
beds furnished a very large amount of from 20 to 50 per cent, 
of ore, having the appearance of melaconite, and giving rise to 
expectations that were always shattered after passing through 
this rich zone and reaching the lean, unaltered pyrites below. 
This so-called black oxide of the Blue Ridge region t seems to be 
an intimate mixture of glance, oxide, carbonate, and sometimes 
finely divided native copper. Two analyses, by Dr. A. Trippel, 
show their constituents: 


* An average sample of thirteen tons of concentrates, taken by the 
author at Santa Rita, in 1881, and partially analyzed under his supervision, 
gave, after continuing the concentration by hand to almost complete re¬ 


moval of the rock constituents : 

Oxides of copper. 13 M2 

Carbonates of copper. 1-27 

Oxides of iron. (P13 

Metallic iron (from stamps). (P29 

Sulphur. O’ll 

Insoluble residue. 0’37 

Metallic copper. 83‘66 

Zn, Ag, Co, Ni, Pb, Mn.Traces 


99.25 


This analysis presented points of considerable difficulty, especially in 
determining the amount of oxide of copper in the presence of metallic cop¬ 
per. Entirely satisfactory results were not obtained; but the method pro¬ 
posed by W. Hampe, by means of nitrate of silver, yielded the only figures 
that could lay the slightest claims to accuracy. 

t Pyrites Deposits of the Alleghanies, by A. F. Wendt. 













DESCRIPTION OF THE ORES OF COPPER. 


3 


Oxide of copper. 5*75 3-80 

Sesquioxide of iron. 1-50 -63 

Sulphur. 18-75 25'40 

Copper. 71.91 41 -00 

Iron. 93 26 "56 

Soluble sulphates of copper and iron. -72 1-78 


99-56 99-17 

A pile of sucli ore, laid on a bed of cordwood and moistened, 
often ignites the wood below, and thus roasts itself without firing. 

Malachite, Cu 2 0, C0 2 + HO; 71*9 CuO, 19*9 C0 2 , 8*2 HO. 

This is a much more valuable compound of copper than the 
two preceding oxides, from a commercial standpoint; although 
no mines in the United States furnish malachite of sufficient 
purity to fit it for ornamental purposes. 

While it may be said to occur in widely distributed but ordi¬ 
narily in non-paying quantities, in the upper decomposed regions 
of most copper deposits, there are certain localities in which it 
forms the principal ore of this metal. It is very seldom found 
in a state of purity, but is mixed with various salts of lime and 
magnesia, oxides of iron and manganese, silica in its various 
forms of quartz, chalcedony, flint, chert, and jasper, and when 
seemingly present in large quantities, it often forms only worth¬ 
less incrustations, or merely colors green nodules and masses of 
valueless material. It is then difficult, and in some cases impos¬ 
sible, to form any accurate opinion of the tenor of the ore from 
its external appearance. 

Azurite, 2CuO, C0 2 + HO; 69*2 CuO, 256 C0 2 , 5*2 HO. 

This mineral requires only a passing notice. It is distributed 
in the same manner and occurs under the same conditions as its 
sister carbonate, but in very much smaller amounts. It occurs 
in profitable quantities only in some of the Southwestern mines. 
Specimens of this mineral are found with malachite and calc-spar 
in the Longfellow mine, exceeding in beauty anything of the 
kind that is known elsewhere in the United States. 

Chalcopyrite, Cu 2 S, Fe 2 S 3 ; 344 Cu, 30'5 Fe, 35T S. 

This is by far the most widely distributed ore of this metal, 
and furnishes the greater proportion of the world’s copper. It 










4 MODERN AMERICAN METHODS OF COPPER SMELTING. 

occurs principally in the older crystalline rocks, frequently ac¬ 
companied with an overwhelming percentage of iron pyrites, in 
bedded veins in Newfoundland, in Quebec, Canada, in Vermont, 
Virginia, Georgia, Tennessee, and Alabama. 

The value of copper-bearing fissure veins below the limit of 
surface decomposition is nearly always due to this mineral. In 
some localities the chalcopyrite forms with pyrite a fine-grained 
mechanical mixture, varying in color with its percentage of cop¬ 
per from deep yellow to steel-gray. This substance is easily rec¬ 
ognized under the microscope as a mechanical mixture, and not 
a chemical compound. In most of the carbonate mines of the 
Southwest that have attained any considerable depth, chalcopyrite 
is already becoming apparent, in minute specks; and it is highly 
probable that the altered ores near the surface, with their valuable 
admixture of ferric oxides, are all due to the decomposition of 
this mineral. The sulpliureted fissure-veins of the Rocky Moun¬ 
tains and Sierra Nevada are seldom free from this mineral, 
although their value almost invariably depends upon their pre¬ 
cious metal contents. The remarkable purple ores and copper 
glance of Butte City, Montana, have already in several mines 
given place in depth to the universal yellow sulphide. 

Chalcocite, Copper Glance, Cu 2 S; 797 Cu, 20-3 S. 

# 

This ore is seldom found in a condition of perfect purity, its 
valuable component being frequently in part replaced by iron 
and other metals. Its copper percentage rarely falls below 55, 
and even at this low standard the mineral retains its physical 
characteristics, a slight diminution in its luster being the princi¬ 
pal difference observable. When high in copper, it greatly re¬ 
sembles the white metal of the smelter. Chalcocite containing 
from 60 to 74 per cent, of copper occurred also pure and is relied 
on in the noted Anaconda mine, Butte, Montana. Several of 
the other Butte mines carry the same mineral, although, as they 
approach the western boundaries of the district, it gradually 
passes into bornite or peacock ore. It is also an important ore 
in Arizona, occurring in large quantities near Prescott, as well 
as in the Coronado and other Clifton mines. In New Mexico, it 
constitutes virtually the entire value of the Nacimiento and Oscura 
Permian beds. It occurs frequently in Texas in the Grand Belt 
mines, and is the principal ore of numerous narrow fissures in 


DESCRIPTION OF THE ORES OF COPPER. 


5 


the Middle and Atlantic States. In the Orange Mountains of 
New Jersey, examined by the author, it was found in a species 
of shale, as an ore of the following composition: 

Copper.75’20 

Iron. 4'10 

Manganese. 1*13 

Silver (2*37 ounces).... (P01 
Gold.Trace 

Bornite or Erubescite, 3Cu 2 S, Fe 2 S 3 ; 55*58 Cu, 16*36 Fe, 

28*06 S. 

This is one of the most beautiful of the sulphureted ores of 
copper, being characterized in its fresh condition by a superb 
purplish-brown color, which soon changes on exposure to the 
air into every conceivable hue, from a golden yellow to the deep¬ 
est indigo, and from a brilliant green to a royal purple. The 
mode of occurrence of this mineral and its limited extent of dis¬ 
tribution as regards depth indubitably stamp it as a product of 
decomposition, solution, and re-deposition of the metallic portion 
of the vein. Like copper glance, this mineral is far from uni¬ 
form in its composition, varying in richness from 42 to nearly 
70 per cent, of copper without entirely losing its characteristic 
colors. 

It forms one of the principal ores of the Butte mines in their 
rich zone, which lies between the leached-out surface zone and the 
unaltered low-grade sulphides below. 

Tetrahedrite, Gray Copper Ore, Fahlore (Cu 2 S, FeS, ZnS, 
AgS, PbS) 4 (Sb 2 S 3 , As 2 S 3 ) j 30*40 per cent. Copper, 

Except in those rare and highly argentiferous varieties in 
which the copper is replaced to a greater or less extent by silver, 
this is seldom regarded in the United States as an ore of copper. 

Both its scarcity and its obnoxious components (arsenic, an¬ 
timony, etc.) prevent its use as a source of copper in this country, 
where the extreme purity of our ores has established such a high 
standard for this metal. Only the most favorable circumstances, 
mineralogical, metallurgical, and commercial, would render the 
working of non-argentiferous fahlores at all practicable. This 
mineral occurs in small quantities in certain of the Butte copper 
mines, rendering their product slightly inferior to that from the 


Sulphur.17-97 

Insoluble. 1-10 


99-51 










6 MODERN AMERICAN METHODS OF COPPER SMELTING. 

oxidized ores of Arizona or the pure sulphides of Vermont. This 
slight disadvantage is, however, far outweighted by their con¬ 
tents in silver, which doubtless owes its presence to this same 
arsenical mineral. From the San Juan region, Colorado, an ar¬ 
gentiferous tetrahedrite adds a notable quantity to the production 
of the United States. It appears principally as matte from the 
lead furnaces, and as black oxide from the Argo separating 
works. 


CHAPTER II. 


DISTRIBUTION OF THE ORES OF COPPER. 

The ores of copper are widely distributed over the earth’s 
surface, and may be found in almost every geological formation ; 
but the deposits of commercial importance had their origin, for 
the most part, at a very early period of the world’s history. The 
mines of the old world, as well as those of Chili and Australia, 
having been described with great minuteness by various careful 
authors, there remain to be mentioned in this place only the prin¬ 
cipal copper districts of North America, which, for convenience 
of description, may be classed in four groups: 

I. The Atlantic coast beds. 

II. The Lake Superior deposits. 

III. The mountain system of veins. 

IY. The Southern carbonate deposits. 

I. THE ATLANTIC COAST BEDS. 

Throughout its whole extent in North America, the Atlantic 
coast is bordered by a succession of parallel ranges, which, by 
their general geological as well as geographical analogy, must be 
classed in the same system. They form an unbroken chain from 
Florida to Labrador, and thence, continuing their same north¬ 
easterly direction along the coast of that bleak country, dip be¬ 
neath the waters of Baffin’s Bay, where they are represented by 
a series of submarine peaks, and, nourishing the gigantic glacier 
system of Western Greenland,* terminate, so far as known, in 
Mount Edward Parry, north latitude 82° 40'. Dr. T. Sterry 
Hunt’s admirable researches have given us a very clear insight 
into the origin, formation, and structure of this immense range 
of mountains within the confines of the United States and 
Canada. It consists essentially of metamorphic rocks—largely 


* See Dr. Kane’s Arctic Expedition for soundings taken in Baffin’s Bay; 
also Geology of Greenland''s Mountains. 



8 MODERN AMERICAN METHODS OF COPPER SMELTING. 

crystalline schists—and is metal-bearing to a greater or less de¬ 
gree throughout its entire extent, though oidy in a few places is 
copper found in a sufficiently concentrated form to justify any 
attempts at extraction. 

The only copper mineral of importance in this range is chal- 
copyrite. In the more northerly division, where there has been 
extensive glacial denudation, this reaches unaltered almost, or 
quite, to the grass-roots, while from Virginia to Tennessee, where 
abrasion has not taken place, and where oxidation has been as¬ 
sisted by climatic influences, decomposition with subsequent con¬ 
centration is found to a considerable depth. The result of this 
is usually a zone, rich in an impure black oxide of copper con¬ 
taining a certain proportion of sulphur, which sometimes occurs 
in considerable quantities near the surface, after first passing 
through a greater or less extent of barren iron oxide, derived 
from pyrite, and which has no doubt furnished the copper to en¬ 
rich the underlying zone. 

The occurrence of this valuable mineral in merchantable 
quantities has, in more than one instance, raised expectations 
and led to large expenditures that have subsequently proved en¬ 
tirely unwarranted; for at a slightly greater depth, the unaltered 
vein assumes its true character of a more or less solid pyrite and 
pyrrhotite, carrying a very small amount of copper (seldom 
above three per cent.) in the form of the common yellow sul- 
pliuret. When the accompanying mineral is a bisulphide of iron 
and the locality is favorable, the pyrite may be utilized in the 
manufacture of sulphuric acid, the copper being extracted from 
the residues by well-known methods; but when the prevailing 
mineral is the wmnosulphide—magnetic pyrites—there can be no 
question of profitable working, pyrrhotite being absolutely value¬ 
less since copperas has become a by-product of fence-wire mak¬ 
ing. At Capelton, in Canada, at Ely, Vermont, and at one or 
two points in Newfoundland, copper pyrite occurs in a suffi¬ 
ciently concentrated form to yield from five to six per cent, in con¬ 
siderable quantities, an ore on which profitable operations may 
be conducted, under favorable conditions. 

In Virginia, at Ore Knob, North Carolina, at the Tallapoosa 
mine, in Georgia, and at Stone Hill, Alabama, indications of a 
similar concentration of copper have given rise to extensive ex¬ 
plorations, and, in some cases, to the expenditures of large 


DISTRIBUTION OF THE ORES OF COPPER. 9 

amounts of money, which have not always resulted satisfactorily. 
These are all examples of so-called bedded veins , following the 
hues of stratification, and being simply sandwiched in between 
the layers of rock. One of the most curious features of these 
beds is the alternate occurrence of the sulphide of iron that forms 
the great mass of the gangue, as pyrrhotite and pyrite. In 
Capelton, for instance, we have the bisulphide; a hundred miles 
distant, at Ely, the monosulphide alone exists; in Virginia and 
at Ore Knob, the monosulpliide preponderates; while in the Tal¬ 
lapoosa mine, the bisulphide alone is found. Neither the chem¬ 
ical nor geological composition of the corresponding country-rock 
explains this phenomenon. Here, it will be proper to mention 
the occurrence, in stratified rocks, of the sulphide of copper (cop¬ 
per glance), usually in unimportant quantity, throughout Penn- 
svl vania, New Jersey, and other Middle and Southern States. 

Aside from a number of shipments of from ten to fifteen per 
cent, pyritous ore from Newfoundland to England, and a few 
hundred tons of copper produced at Strafford, Vermont, the only 
important contribution that this group furnished to the world’s 
metal market for the year 1884 was 2,260,000 pounds from the 
Canadian group of pyrites beds. A few tons of this metal from 
the Maine mines, and an equally insignificant amount from cer¬ 
tain unimportant private enterprises, appear to complete the rec¬ 
ord for group No. I. 

In 1885, the Canadian product was slightly increased, while the 
Vermont and New Hampshire mines greatly diminished then- 
output. Up to 1890, the production of Canada has not been 
materially increased. 

II. THE LAKE SUPERIOR DEPOSITS. 

These have excited such universal interest, from their unique 
character and their great commercial importance, that there is an 
abundance of correct and detailed information concerning them 
in the pages of the Engineering and Mining Journal, the Reports 
of the United States Geological Survey , the Transactions of the 
American Institute of Mining Engineers , and in various other 
publications easily accessible to the student. 

The grade of the ore furnished by these extensive conglom¬ 
erate deposits is very low, ranging from three-quarters of one 
per cent, of copper to about one and three-fourths per cent., save 


10 MODERN AMERICAN METHODS OF COPPER SMELTING. 


in the case of the Calumet & Hecla, whose extraordinary extent 
and richness—four and one-half per cent.—make it a remarkable 
exception. The figures just mentioned are so low in comparison 
with the percentage of many less profitable sulphuret mines that 
it is necessary to explain to those not familiar with the subject, 
that the occurrence of the copper in the Lake mines in a native- 
or metallic state permits the substitution of an inexpensive me¬ 
chanical concentration for the costly series of calcinations and 
fusions necessary in the treatment of sulphide ores. In the case 
of the Lake ores, a single crushing and washing removes the 
gangue rock almost completely, leaving the metal in such a condi¬ 
tion that a single refining process fits it for use, and yields, in the 
absence of sulphur, arsenic, or other impurities, a copper of the 
best quality, which commands the highest price in the market. 

The production of this group of mines is very large, and 
shows a steadv increase. For the year ended December 31,1884 r 
it aggregated 69,353,232 pounds of pure copper, which in 1885 
was increased to 72,148,172 pounds, while the striking of the 
Calumet & Hecla vein at a great depth by the Tamarack Com¬ 
pany promises an important addition in the future to these al¬ 
ready large figures. The Lake production in 1889 was 86,139,000 
pounds, and in 1890, 99,570,000 pounds. 

Regarding these mines from an economic standpoint, we find 
that the veins producing the great masses of native copper, for 
which this district is so celebrated, have not proved so persistent 
nor so uniformly profitable, as the veins in which the copper is de¬ 
posited in more minute particles. 

A totally different series of mines were those that were started 
in the porphyritic diabase, that is an important and persistent 
feature of the geology of this part of the country. 

These so-called “Ashbeds ” carry more or less copper through¬ 
out a very great extent, but are only rich enough to pay for 
working within a small area. 

The Kearsarge, Wolverine, Pewabic, Franklin, and Atlantic 
are, or have been, noted producers of copper from these ashbeds. 
But the best known of the entire lot is the Quincy mine, which 
differs greatly from most of the other amygdaloid beds in carry¬ 
ing nearly half its copper in comparatively coarse fragments,, 
though in nowise resembling the “ masses ” of the group immedi¬ 
ately preceding. The average yield of the Quincy ore is 2 per 


DISTRIBUTION OF THE ORES OF COPPER. 


11 


cent., and as this mine has already reached a depth of about 4,000 
feet on an incline, it shows how little weight need be attached to 
the fear of greatly increased costs as depth is gained. Of course, 
if there is much water to be pumped to the surface, the condition 
becomes different. 

The celebrated Atlantic is also an amygdaloid mine, and is 
situated very near the Quincy. It has a world-wide reputation 
of having brought the costs of mining and mining down to the 
lowest conceivable point of economy. Its yield is extremely uni¬ 
form, usually averaging 0‘75 per cent. Last year it dropped to 
0'6 per cent., which is only 12 pounds copper to the ton 
of ore. 

This, at 15 cents per pound, would represent a gross cash 
yield per ton of $1.80. Out of this small amount must come 
the cost of mining from a depth of 1,600 feet j of constant and 
very extensive development of ore; of crushing through a com¬ 
paratively fine screen, and concentrating the copper into a 70 or 
80 per cent, product fit for the smelter; of freighting this prod¬ 
uct to the smelter, and paying a comparatively high price for 
the single furnace operation, which is a combined smelting and 
refining j of transporting the ingot copper to a market at a great 
distance, of selling the copper, and of the general office and 
managing expenses. And last of all, though by no means least 
important, of paying the dividends to its stockholders. 

The Atlantic mine and its management present an excellent 
subject for contemplation by the owners of many Western cop¬ 
per and silver properties. Not that its methods can be always 
followed, or that its own manager and foremen, confronted with 
the difficulties of mines and ores that are unfamiliar to them, 
make a better showing than other men, as many unfortunate in¬ 
vestors that have pinned their faith on Lake Superior mining 
captains, have learned. But the strict economy and system here 
practiced, and indeed rendered necessary by the struggle for ex¬ 
istence, may be copied with immense advantage by the majority 
of the Western. 

The mines that at the present time are the great copper pro¬ 
ducers of the Lake region are those that are following out one of 
the several well-known but otherwise comparatively barren, con¬ 
glomerate beds. 

The first corporation to demonstrate that these beds were, in 


12 MODERN AMERICAN METHODS OF COPPER SMELTING. 

places, commercially valuable, was the well-known Albany and 
Boston Mining Company, in 1863, I believe. 

Its success w T as only of short duration, but was soon followed 
by the organization of the celebrated Calumet & Hecla Company r 
in 1865, one of the most profitable mining ventures of modern 
times in proportion to the money paid in at the start. 

The Allouez, Osceola, Tamarack, and Tamarack Junior are 
the other principal conglomerate mines, though the Osceola for 
several years has transferred its attention to an amygdaloid bed 
that crosses its territory. 

The Calumet & Hecla had the extraordinary good fortune to 
include within its original boundary lines the largest and most 
important portion of the only really profitable conglomerate bed 
ever known in the Lake region. Although this bed extends for 
a great length, and is a prominent feature in the geological land¬ 
marks of the district, it is only for a length of about three miles- 
along its strike that it is profitable. The Calumet & Hecla hap¬ 
pened by great good fortune to sink its first shaft almost exactly 
in the center of this magnificent and almost unparalleled ore-cliute. 
Some seventeen shafts have been sunk along the outcrop of this 
vein, and an extreme depth of 3,800 feet has been reached on an 
incline. This incline, or, in miners’ parlance, “ dip,” being 37£ 
degrees, the greatest perpendicular depth is about 2,310 feet. 
This point is between the 29th and 30th level, and as, in spite of 
this great depth, there is no excessive heat, we can see no reason 
why depths may not be reached in this mine to far exceed any¬ 
thing yet attempted in subterranean work. Of course it will de¬ 
pend mainly upon the extent in depth of the ore-chute, which 
has never yet shown the slightest indication of either weakness 
or poverty. 

Many mining men do not understand how it is possible for 
the Tamarack Company to have tapped the Calumet & Hecla 
vein below its [then] deepest workings, by means of a perpen¬ 
dicular shaft, when United States mining laws allow each owner 
to follow his vein in depth indefinitely, following all its dips and 
angles, and regardless of whose surface ground it may run under. 

And, indeed, this remarkable enterprise in prospecting would 
not have been possible had the State of Michigan been under the 
control of the United States Mining Code. 

But most of the older States have their own mining regula- 


DISTRIBUTION OF THE ORES OF COPPER. 


13 


tions, and Michigan, in common with many others, has decreed 
that mining lands shall be bounded as any other lands; that is, 
by vertical lines, or rather, by lines running toward the center 
of the earth. Therefore, if a vein pitches at all from the perpen¬ 
dicular, it is evident that in time it vail pitch outside of the 
boundary lines of any tract, however large, and the extreme 
regularity of pitch and value in the Calumet & Hecla bed 
tempted the Tamarack people, who owned a tract into which this 
bed must penetrate at a certain depth, to sink a vertical shaft to 
cut the bed at this great depth. The shaft was sunk with great* 
rapidity and skill to a depth of 2,275 feet, at which point it cut 
the Calumet conglomerate bed in all its richness, as had been 
anticipated, and ever since, the Tamarack has been a large and 
profitable producer. 

But it must not be understood that the Calumet & Hecla is 
throughout its entire course cut off by the Tamarack at this com¬ 
paratively slight depth. If so, its career would already be nearly 
run, and it could not possess the deep workings above described. 
It is only a comparatively small tract of the Tamarack Company 
that thus thrusts itself into the Calumet grounds, though further 
explorations have opened up enough territory to insure a long 
and profitable future of the newer enterprise, as well as the older. 

The occurrence of native copper at the Ray mine in the little 
Canyon of Mineral Creek, which empties into the Gila River just 
below the town of Riverside, Pinal County, Arizona Territory, 
attracted considerable local interest at one time. 

But, mineralogically speaking, it possesses but little interest, 
as the native copper results simply from the decomposition of 
sulphides or similar compounds. 

The mine consists of a strong dike of diorite, which on cool¬ 
ing has become so cracked and fissured, that on its subsequent 
permeation by watery solutions carrying copper, this metal has 
been deposited in a thin film on every surface of these innumer¬ 
able cracks and planes of fissure. This saturation with mineral 
salts has also decomposed the diorite to a high degree, changing 
it into a softish material, resembling steatite. It is only in cer¬ 
tain limited areas that the metallic copper becomes at all a marked 
feature, but in one certain winze, between the 50 and 100-foot 
level, it presents a most tempting appearance, the sheets of native 
copper being so thick and numerous that it is actually difficult to 


14 MODERN AMERICAN METHODS OF COPPER SMELTING. 

mine the rock, and, after much difficulty, I have taken out pieces 
myself, weighing fifty pounds or more, that were simply a frame¬ 
work of native copper, tilled in with diorite, and certainly con¬ 
taining 30 per cent, or more of that metal. Unfortunately these 
rich chutes are very limited, in depth as well as horizontally, 
the main value of the mine depending upon its immense masses 
of low-grade ore which, near the top, consists of carbonates and 
oxides, but within a hundred feet from the surface, changes into 
copper-glance, which tills the minute fissures of the diorite in the 
manner already described. A more interesting mine for the 
geologist or student of vein formation can hardly be imagined. 
It is mentioned in connection with the Lake mines solely on ac¬ 
count of its native copper. 

While speaking of the distribution of copper in a metallic 
form, it seems best also to include the native copper deposits of 
Santa Rita, New Mexico, which differ so radically from other 
members of the group in which they geographically belong, that 
they must be regarded as unique. 

In the southwestern corner of New Mexico, a large but ill-de¬ 
fined tract of land is overlain by porphyry, which, although ap¬ 
parently homogeneous, is in reality of several varieties, only one 
of which is metal-bearing. It is only where this particular for¬ 
mation comes to the surface that the rock is found heavily stained 
with the salts of copper; and on being followed beyond the limit 
of destructive atmospheric influences, it carries a fair but very 
variable percentage of copper in sheets, nodules, threads, etc. 

The most striking difference between these deposits and those 
of Lake Superior is in the degree of decomposition of their me¬ 
tallic contents. In the Santa Rita deposits, this decomposition 
has progressed to such an extent as to have transformed the en¬ 
tire nodule of metal into an oxide or carbonate, the red oxide— 
cuprite —greatly predominating, while the two carbonates occur 
chiefly as stains and films. Even such pieces of metal as seem 
to have escaped oxidation, and to have retained their original 
form and appearance, are found, on close examination, to consist 
of numerous thin plates of metal, separated by a layer of oxide, 
while the entire mass is so thoroughly decomposed that little 
difficulty is experienced in grinding the greater proportion of it 
into a powder. 

This condition of the ore naturally produces a most unfortu- 


DISTRIBUTION OF THE ORES OF COPPER. 


15 

nate complication in the subsequent process of mechanical con¬ 
centration, and leads to enormous losses, especially when stamps 
are used for crushing' the ore. 

III. THE MOUNTAIN SYSTEM OF VEINS. 

In this group are all the deposits of copper occurring in the 
Rocky Mountains and Sierra Nevadas north of the great carbon¬ 
ate districts of Arizona and New Mexico. 

It is an uncertain division, geographically speaking, and un¬ 
satisfactory geologically, as it contains a heterogeneous collection 
of mines and minerals, scattered over an immense and ill-defined 
tract of country. An enumeration and very brief notice of the 
few great centers of commercial importance will also include a 
sufficient diversity of ores to serve as types for the whole. 

Most northerly, and by far the most important of all, are the 
deposits at Butte City, Montana.* The copper minerals occur 
here in a granite formation, in some places approaching gneiss in 
structure and appearance. The veins are undoubtedly true 
fissures, and constitute two groups of different geological periods, 
crossing each other at an angle of about 60 degrees, although no 
exploration has been done at the points of intersection. The 
east and west veins have been explored to a much greater ex¬ 
tent than those of the other group, and are apparently of much 
greater value. They are of unusual width, from 5 to 40 feet, 
perhaps averaging 7 feet, and vary greatly in pitch, although 
usually approaching the vertical. They seem to stand in some 
constant relation to an accompanying band of a decomposed ma¬ 
terial resembling porphyry, varying in width from *100 to 1,000 
feet, and near the longitudinal axis of which they are situated. 

The east and west veins are alone worthy of particular notice 
in this place. They vary among themselves in the minerals that 
constitute their value. The Anaconda and neighboring proper¬ 
ties carry in the decomposed zone chiefly a copper glance of 
greater or less purity, while the Parrot portion of the great vein, 
with its satellites, yields principally an ore resembling bornite 
(peacock, or horseflesh ore), which varies greatly in its chemical 

* For a detailed description of the mines and metallurgical works of this 
district, see a paper by the author, entitled “The Mines and Reduction- 
Works of Butte City, Montana.” United States Geological Survey , Mineral 
Resources, Albert Williams, Jr., 1885. 



1G MODERN AMERICAN METHODS OF COPPER SMELTING. 

composition. A striking feature of these veins is, that they carry 
little or no copper for a space of from 50 to 500 feet (average 
about 250 feet) from the surface down to water-level, when the 
rich minerals already described appear suddenly, changing from 
poverty to wealth in the space of a few feet, instead of gradually, 
as is usually the case in other districts. 

This rich zone has evidently derived its principal value from 
the leaching out of the surface portion of the vein, and its un¬ 
usual extent may be inferred from the fact that many of the 
workings have penetrated it for 300 feet or more, without find¬ 
ing any serious diminution in its copper contents; but some of 
the large mines have already worked through it into the unal¬ 
tered ore of corresponding low grade.* 

The average value of the second-class Butte ore, as extracted, 
is about 10 per cent., and perhaps one ton in ten is set aside as 
first-class, averaging 30 per cent. The second-class ore is well 
suited to mechanical concentration, the principal drawback being 
the accompanying pyrite, which, though valuable as a flux, pre¬ 
vents the production of so rich a concentrate as economy would 
dictate, and adds materially to the expense of calcination. An 
important commercial advantage is enjoyed by the owners of the 
Butte mines in the silver that occurs in amounts varying from 
one to four cents for each pound of copper. Some 18,000 tons 
of such ore, smelted under the charge of the author, yielded, ac¬ 
cording to the assays on which the product was sold, 0*5757 
ounce of silver to each per cent, of copper, or 3|- cents silver, at 
$1.10 per ounce, to each pound of copper. 

As the silver was not leached out with the copper from the 
upper portions of the vein, it follows naturally that the re-depo- 
sition in the rich zone of this vast quantity of non-argentiferous 
copper, would greatly lessen the ratio of the more valuable metal 
to the copper. Further, that if this reasoning were correct, we 
should expect the unaltered ores in depth, and that were not di¬ 
luted with extraneous copper, to be proportionately richer in sil¬ 
ver than the ores from the rich copper-zone. And this is found 
to be the fact as far as the unaltered zone has been penetrated. 

In order to give some idea of the percentage of these ores at 

* The writer desires to acknowledge the assistance of Mr. James E. 
Mills in preparing his brief statement of the geology of the Butte copper 


mines. 



DISTRIBUTION OF THE ORES OF COPPER. 


17 


the present time, I quote from the reports of the Boston and 
Montana Company, published for the year 1890. The actual yield 
of all the ore mined and treated by this corporation for that year 
was 9‘36 per cent., and the copper produced aggregated 26,942,- 
298 pounds. But this is a very high average, a large proportion 
of the yield having been derived from the rich, altered ores. 

The yield of the Anaconda and affiliated mines, as obtained 
by Mr. James Douglas by comparing the amount of ore reported 
by this company to have been transported to its works with its 
copper production, was 5*9 per cent.; and as considerable rich, 
altered ore was worked during the year, it is evident that, in the 
near future, all the Butte mines must prepare to handle an ore 
that does not average above 5 per cent, in copper, and possibly 
5 ounces in silver. Whether this can be done at the present rate 
of wages, fuel, and transportation, remains to be seen. 

An almost exactly analogous occurrence of these rich purple 
ores gave originally that great impetus to mining that has placed 
Chili, up to a recent date, at the head of the copper-producing 
countries of the world, and a steady, though by no means rapid, 
improvement in practice and apparatus has enabled her to main¬ 
tain her output, even though the rich, altered ores have been long 
since exhausted, and have given place to the 7 or 8 per cent, 
pyritous material that forms the normal filling of these and most 
other copper veins. The complete disappearance of the more 
valuable mineral occurs at a depth of about 500 feet in the deep¬ 
est Chilian mine on record, the Pique mine. 

The product of the Butte district for the year 1884 is closely 
estimated at 41,500,000 pounds; for 1885, 67,798,864 pounds, 
while in 1889 it was increased to 104,200,000 pounds, rising for 
1890 to 122,950,000 pounds. 

The remainder of No. III. group is of a miscellaneous charac¬ 
ter, geologically, mineralogically, and geographically. . 

The next most noteworthy occurrence of copper is in the fis¬ 
sure-veins of Gilpin County, Colorado, which traverse a granite 
formation, and are principally important for their value in the 
precious metals. The copper contents rarely exceed 1 per cent, 
of all the ore extracted, or 5 per cent, when only the first-class or 
smelting ore is considered. The gangue is invariably quartz or 
decomposed feldspar, and the metal occurs almost exclusively as 
chalcopyrite, in company with small quantities of zinc-blende, 


18 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


galena, various antimonial and arsenical compounds, and a much 


larger amount of pyrite. 

The new San Juan region promises to add a considerable 
amount of copper to Colorado’s quota. The metal occurs there 
principally as a constituent of argentiferous tetrahedrite. The 
statements of ore-buyers, verified by personal examination, show 


an average tenor of about 3.1 per cent, of copper for the ordinary 
ore as shipped from these mines. Their silver value varies from 
20 to 500—average about 60—ounces to the ton. A limited 
amount of copper is furnished from other districts of Colorado, 
but is in no case mined in sufficient quantities to justify an inde¬ 
pendent business apart from the precious metals, which almost 
invariably constitute 90 per cent, or more of their value, as ex¬ 
pressed by the price received for the ore at smelting-works. The 
product, therefore, is insignificant, and, when added to that of the 


districts already noticed, will not raise the total product of group 
No. III. for 1884 to much above 44,000,000 pounds. In 1890, 
Colorado produced 6,760,000 pounds. 


IV. THE SOUTHERN CARBONATE DEPOSITS. 

It is to this group of oxidized ores that the attention and capi¬ 
tal of business men were principally directed a few years ago, 
and although the deposits of this nature are almost limitless in 
number, and the labor and expense of producing metallic copper 
from minerals that have already been prepared by nature for the 
simple fusion that is alone necessary, are comparatively slight, the 
high expectations formed have seldom been realized. The un¬ 
favorable character of the country, the scarcity of fuel and water, 
the expense of transportation, the distance from central author¬ 
ity, and, above all, the eccentric and uncertain character of the 
deposits, have brought about this result, and the copper market 
has been overloaded, and many valuable deposits exhausted, 
without any corresponding advantages to the promoters. 

The most important mines of this division are all situated in 
Arizona or New Mexico, and differ too much in their character¬ 
istics to permit of any general description. 

In one class of these mines, notably the Copper Queen, the 
copper occurs as carbonates and oxides, associated with oxide of 
iron and ferruginous clays, filling immense caves in the lime¬ 
stone. 


DISTRIBUTION OF THE ORES OF COPPER. 


19 


Iii another class of mines, such as those at Clifton, Arizona, 
the bodies of oxidized ores are irregularly distributed through 
beds of diorite, the occurrence of the ore beds being apparently 
determined by intercalated masses of limestone, which have 
played an important part in either the deposition or alteration of 
the copper, or in both processes. The ore-bodies, although they 
occur within certain limits, were irregularly distributed, and are 
of very variable size, and the alteration has not occurred to any 
great depth. 

Although this class of deposits furnishes a certain amount 
of the very richest ore known to the mineralogist, in the shape 
of streaks, bunches, and even considerable aggregations of red 
oxide and the two carbonates of copper, the average percentage 
of this metal contained in the furnace charges of the most ex¬ 
tensive and profitable smelting establishments belonging to this 
group is not high. A constant yield of 10 per cent, is considered 
very good, and the dividends afforded by certain of these 
properties, laboring under the disadvantages of expensive fuel, 
transportation, etc., result principally from the exceedingly sim¬ 
ple nature of the process employed and the remarkably favor¬ 
able composition of the accompanying gangue rock. This con¬ 
sists usually of a mixture of oxides of iron and manganese, with 
calc-spar, and for the most part contains just about the proper 
amount of silica to form, with the constituents just mentioned, 
an easily fusible slag, and one reasonably free from copper, con¬ 
sidering the unusual practice of producing metallic copper and a 
slag; to be thrown away at the first fusion. In cases where the 
contents in silica exceed the proper amount, very basic ores, con¬ 
taining an excess of the oxides of iron and manganese, can al¬ 
most always be procured in the immediate neighborhood; or, in 
default of this, beds of cpiite pure iron ore and quarries of lime¬ 
stone almost perfectly free from silica are nearly always close at 
hand. The great purity of the metal produced is also a highly 
favorable factor in estimating the relative advantages of this 
group; for, aside from bringing a price nearly equal to Lake 
copper, it is always sure of a ready sale. 

The product of this group, including the small amount re¬ 
ferred to in the succeeding paragraph, as coming from unclassi¬ 
fied sources, may be safely estimated for the year 1884 at 
24,000,000 pounds, dropping in 1885 to 22,706,000 pounds, 


20 MODERN AMERICAN METHODS OF COPPER SMELTING. 

and rising in 1889 to 31,600,000 pounds, and in 1890 to 35,720,- 
000 pounds. 

A considerable number of mines and deposits that cannot be 
consistently brought under any of the four divisions enumerated 
still exist; but aside from certain sulpliureted veins in Nevada 
County, California, which are interesting chiefly on account of 
the method employed for the beneficiation of the ore—leaching 
and precipitation in revolving barrels—and the Walker River 
mines in Esmeralda County, Nevada, but few deposits are 
worthy of note. The Nacimiento copper quarries in Central New 
Mexico,* the Oscura copper-fields in the Oscura Mountains, New 
Mexico,! and the Great Belt copper deposits in Texas present cer¬ 
tain curious and interesting features to both mineralogist and 
paleontologist. The metal in each place occurs in the shape of 
petrifaets of shells, fishes, and palm-leaves, branches, and twigs 
—all changed completely into an impure variety of copper glance, 
and found in that same Permian formation that at Mansfeld, 
Germany, and in the Russian Empire, has been, and still is, so 
prolific in copper. 

Since the preceding paragraph was written, there has been lit¬ 
tle change in the Arizona mines, and but a slight increase in their 
output. 

In describing the principal mines, I shall quote from a paper 
by the President of the Copper Queen mine, than whom there 
is no better authority on the subject.}: 

There are only three groups of mines in Arizona now produc¬ 
ing copper in any considerable amount. These are the districts 
of Clifton, Bisbee, and Globe. 

The Clifton district, in the southeastern corner of the Terri¬ 
tory, so far as production is concerned, is divided between a 
Scotch organization, known as the Arizona Copper Company, 
and the Detroit Copper Company. 

At Globe, in Pinal County, the Old Dominion Company, on 
the old Globe mine, is the only important producer, while at Bis¬ 
bee, in the extreme south of the Territory, the Copper Queen 

* See pamphlet "by F. M. F. Cazin, for a full and accurate description of 
these mines, and estimate of their value. 

t See a paper by the author in the Engineering and Mining Journal of No¬ 
vember 18, 1882, for report on these properties and the surrounding country. 

tTlie “Copper Resources of the United States,” by James Douglas. 



DISTRIBUTION OF THE ORES OF COPPER. 


21 


Company, under its new management, has absorbed by purchase 
most of the surrounding promising claims, though without ever 
finding anything to compare with its original famous deposit, 
which is still largely productive. 

As experience and knowledge have been gained by exploration 
and study, it is found that there is a much closer analogy be¬ 
tween these different deposits than was at first supposed. Oxi¬ 
dized ores of copper are found, to a greater or less extent, 
throughout almost all of the peculiar, abrupt mountain ranges, 
so characteristic of Arizona. And wherever they are found in 
any quantity, an examination of the adjacent rocks is pretty cer¬ 
tain to reveal limestone [probably of the Carboniferous Age, and 
of a thickness varying from a few hundred to 3,000 feet], quartz¬ 
ite, and dikes of some volcanic rock, usually of a porphyritic 
texture. 

The copper ore itself, as Mr. Douglas points out, occurs al¬ 
most invariably in, or very near, this carboniferous limestone, 
which has been mainly influential in effecting the oxidation of 
the ore and the removal of the sulphur with which it was no 
doubt originally combined. This process of oxidation in many 
instances extends to a great depth, for the decomposition of the 
ore itself has furnished solvents that act most powerfully upon 
the limestone, especially at the edges of a shrinkage-crack, or 
wherever they can obtain a point of attack, and on this account, 
water has penetrated the limestone and decomposed its ores to a 
far greater depth than the ores found in the adjacent feldspathic 
rocks. 

In Bisbee the ore is confined exclusively to the limestone, oc¬ 
curring often in chambers of vast size, and which at first were 
supposed to have been caves in the limestone filled with these 
massive deposits of oxidized ores in place, but now are thought 
to have resulted from the gradual decay and solution of the 
limestone, and the interstitial exchange and deposition of an 
atom of the copper mineral in a sulphide form, and which has 
since become oxidized. 

In Clifton and Globe, the ore is not so strictly confined to the 
limestone, but is found mainly in the contact between the lime- 
stone and granite or sandstone. 

A peculiarity of all these mines is the occurrence of some¬ 
times extensive bodies of unaltered sulphide ores, often in the 


22 MODERN AMERICAN METHODS OF COPPER SMELTING. 

higher levels, and surrounded on all sides and below with thor¬ 
oughly oxidized ores. It is difficult to see what causes have been 
at work to prevent their oxidation amidst such universal decay. 

The yield of the. Arizona mines is difficult to get at, as so 
much sorting is done, and so much depends on the cost of freight, 
that only ore above a certain percentage can be profitably de¬ 
livered to the furnace. 

At the Copper Queen, the average yield of the ore smelted is 
8 per cent., but Mr. Douglas tells us that to obtain an ore of this 
grade, nearly an equivalent amount of lean ore is stowed away 
in the stopes. 

The yield at Clifton and Globe is necessarily considerably 
higher, owing to the 100-mile wagon-freighting of the coke to 
Globe, and the fact that the Clifton ores are so siliceous that 
much barren limestone has to be added to the furnace charge. 

The Copper Queen ores, consisting of oxidized copper-com¬ 
pounds, with a gangue of ferric oxide and some alumina and 
silica, are probably as favorable smelting ores as the world has 
ever seen. 

The Verde mine, in the northern part of Arizona, has been at 
times an important producer, and is still considered a most valu¬ 
able property. Much of its value consists in the precious metals, 
which are, however, distributed very irregularly throughout the 
copper ores. 

The ores of this mine in all respects are different, both in oc¬ 
currence and composition, from the Southern carbonate mines. 
They consist of lens-shaped masses in crystalline schists, and are 
oxidized only on the surface, the carbonates being soon replaced 
by the rich altered sulphurets, similar to the Butte ores. 

THE FUTURE OF COPPER IN THE UNITED STATES* 

A careful study of the history and present condition of the 
copper-producing district of the United States, as well as of the 


* This chapter was already completed when I first saw the paper of Mr. 
James Douglas already referred to, on “ The Copper Resources of the United 
States.” My own conclusions so closely resembled his [which, to be sure, 
is not remarkable, as we both reasoned from the same premises], and the 
form in which they were expressed so closely followed his paper, that I have 
thought it best to supplement my conclusions by some new ideas that I 
found in his, and credit the entire paragraph to Mr. Douglas. 



DISTRIBUTION OF THE ORES OF COPPER, 


23 


tracts of country still partly or entirely virgin, where lean, pyri- 
tous ores of copper are known to exist, seems to point to the fol¬ 
lowing conclusions: 

Preserving the geographical distribution of copper that has 
already been adopted in the preceding paragraphs, we have first 
to consider what may be expected from the Atlantic Coast 
beds. 

At present the only copper produced in this district of any 
importance is from the Ely mine, in Vermont, which has awak¬ 
ened from its lethargy, and under more economical and sensible 
management than it has ever before enjoyed, is producing now 
at the rate of something like 1,500,000 pounds annually. This 
all comes from the bottom of the shaft, at a depth of nearly 
3,000 feet on an incline, or about 900 feet perpendicularly from 
the surface. And it is with great satisfaction I can report, from 
late personal observation, that there is not the slightest sign of 
any falling off in either the quantity or quality of the ore at this 
great depth. 

When one reflects that this same great bed strikes through 
the country for many miles, cropping out at intervals, and every¬ 
where showing strong bodies of pyrrhotite, with more or less 
chalcopyrite intermixed, it is surprising that so little exploration 
has been accorded to it, especially as the copper is of extra good 
quality, fully equal to the best Arizona copper. 

The Maine pyrites mines are practically idle, their grade hav¬ 
ing been too low to repay the cost of working. But a slight rise 
in the price of copper would enable several of these mines to 
exist, as well as stimulate the search for others. 

The noted Ore Knob mine in North Carolina has probably 
seen its best days, but vast quantities of low-grade ores are said 
to still exist in the Pyrrhotite mines of Ducktown, Tennessee, 
• and it is probable that these will some day again become pro¬ 
ducers. 

In Georgia and Alabama, there are considerable bodies of 
pyrites suitable for acid-making that will in time, no doubt, add 
their mite to the general production of copper, but it is an un¬ 
fortunate fact, that there is as yet no sign in any part of our 
country of those immense cupriferous masses of iron bisulphide 
that have rendered the Iberian peninsula so famous, and added 
so greatly to the wealth of England. 


24 MODERN AMERICAN METHODS OF COPPER SMELTING. 


The copper-bearing slates and sandstones of Pennsylvania 
and New Jersey, and the fissure veins of Maryland, are but small 
affairs, and unless greatly augmented by future discoveries, can¬ 
not be considered as of the slightest importance in the future of 
the metal under consideration. 

Unless, therefore, some radically new, and as yet unsuspected, 
source of copper-production is discovered, a most unlikely con¬ 
tingency, we cannot look to the Atlantic Coast for any consider¬ 
able supply of copper in the future. 

If this district possessed gigantic veins or beds of iron pyrites, 
even quite low in copper, we might expect in time a large pro¬ 
duction of the more valuable metal from this source, as the total 
production of our sulphuric acid therefrom would only be a 
question of time. 

But they apparently do not exist, and even to-day it is found 
cheaper to import cupriferous pyrites for acid-making from the 
Spanish mines than to use our own less favorable and non- 
cupriferous material, which also has to stand railroad transporta¬ 
tion instead of the far cheaper ocean-freight. 

Nor do the carbonate deposits of the Southwest promise to 
be any factor of increasing importance to our copper industries. 

Not a single new mine of importance has been opened since 
the davs of the old mines already described, and to which Arizo- 
mbs fame is due. Not but that there are many scattered deposits 
of local importance throughout her vast extent of copper-bearing 
rocks that, in the aggregate, will produce considerable copper for 
an indefinite period. But no one district can be selected that is 
at all likely to surpass those now in operation, and they them¬ 
selves are already straining their resources, and feeling the need 
of every possible advantage accorded to them by the cheaper 
freights and fuel of the present day, to offset the lower grade 
of their ores, the increased expenses of deep mining, and the 
extensive exploratory work essential to their existence. To 
these expenses, the cost of pumping on a large scale will, no 
doubt, be added when a certain depth is reached, and Arizona 
can hardly be counted on to materially increase her output in 
the future, although she may hold her own for many years, even 
this fact depending mainly upon the ruling price of copper. 

Although the ores of the Copper Queen have remained quite 
thoroughly oxidized to an unusual depth, and still show no signs 


DISTRIBUTION OF THE ORES OF COPPER. 


25 


of changing’, this is by no means the usual rule of this Territory, 
and most of the mines, before reaching a great depth, will lose 
the enormous advantage that they now mostly possess, of having 
their calcining done by Nature, and being able to produce cop¬ 
per by a single fusion of the simplest character. 

What has just been said of the Arizona mines applies in a 
general way, and on a much larger scale, to the more important 
Montana mines; the cream of the Butte district has already been 
skimmed, and the less valuable portions only remain for the 
future. 

This lowering of value will be partly offset by greater skill 
and economy in mining, and especially in treating, the ores in 
the future, and the larger companies, notably the Anaconda, 
with its affiliated Chambers Syndicate, as well as the Butte and 
Boston and Boston and Montana companies, have wisely ob¬ 
tained possession of large tracts of ground that is still virgin, 
and to a greater or less extent on the strike of the great ore- 
course that gives Butte its value. 

The enormous plant of the Anaconda Company, when it gets 
fairly into the valuable ground that lias for the past few years 
been inaccessible on account of the fire, together with the new 
and extensive plant of the Boston and Montana Company at 
Great Falls, and the tendency of all the existing works to in¬ 
crease their capacity, will probably, for a time, augment the out¬ 
put of copper from this district, almost regardless of the market 
price of this metal. For, if the price is low, the companies have 
to increase their output to pay any profit at all; while if the 
price is high, they naturally strain every nerve to take advantage 
of the favorable circumstances. 

But the end is certain. Like the great carbonate mines 
of Leadville, they will soon exhaust their rich, decomposed ores, 
and have to fall back on their lean, unaltered sulphides, handi¬ 
capped at the same time with the increasing expenses of deep 
mining. 

But, like Leadville, they will learn to grapple with the diffi¬ 
culties of the situation, and it is quite probable that, with lower 
wages, cheaper freights, and improved and economically managed 
plants, they will derive more profit from a 6 per cent, ore at the 
thousand-foot level than from one of double that percentage at 
the surface. 


26 MODERN AMERICAN METHODS OF COPPER SMELTING. 

It is not probable that any man who saw the rise of Butte 
City will live to witness its fall as an important and remunerative; 
copper-producer. 

As regards Colorado and the rest of the great Mountain Sys¬ 
tem, in which I have included all of the far West, except the 
strictly local Arizona carbonate deposits, there can be nothing 
said with any certainty, or even probability, excepting that we 
have no reason to look for any great increase of copper produc¬ 
tion. Colorado holds its own, its copper occurring principally as 
a by-product of the gold and silver ores, for which this State is 
so famous. 

We frequently hear prophecies of the discovery of some new 
copper-district in the heart of the great Mountain System of the 
Rockies or Sierras, before which Butte and Arizona will retire 
abashed, and even the steady flame of Lake Superior’s production 
will wane. 

But, as I had written a year ago, and am happy to see sub¬ 
stantiated by such an authority as Mr. Douglas, such a discovery 
is in the highest degree improbable. 

Of all the metals, copper is the most obtrusive and the most 
bold in betraying its presence. A few ounces of its decomposed 
compounds will stain a whole mountain-side green or blue, and 
a very small quantity will so affect, the waters of all streams run¬ 
ning over it, especially in the dry season, that the attention of the 
prospector is immediately attracted to the fact, and he is sure to 
find out the cause. 

There are no such hidden recesses in this country as are popu¬ 
larly supposed to conceal these wonderful deposits. Possibly 
within the heart of the lava beds in Oregon, or in some of the re¬ 
moter and more inaccessible depths of the Dakota “ Bad Lands,” 
there may be a few square miles where the foot of prospector has 
not yet penetrated. But that is only because these districts are 
well known to contain no valuable minerals. 

Wherever there is the least chance of the occurrence of ores, 
and ten thousand wild places where there is not, the prospector 
has penetrated over and over again, until every nook and corner 
of our mountains is as familiar to some one or more mining 
men, as are the streets of a city to one who is born there. 

It has been my lot to spend many months during the past 
twenty years in the mountainous districts of new mining re- 


DISTRIBUTION OF THE ORES OF COPPER. 


27 


gions; but I cannot recollect that I ever yet wished to visit any 
valley, no matter how remote, nor any mountain peak, how¬ 
ever inaccessible, that I could not have found a guide, who 
knew every foot of the ground, and had broken, with his pros¬ 
pecting pick, samples from almost every promising ledge or for¬ 
mation. 

There are many districts, especially within the limits of Utah, 
California, and Nevada, that to-day offer flattering inducements 
for examination, and no doubt, in the aggregate, will produce 
many million pounds of copper within the next decade, but there 
is no reason to expect any overwhelming flood of this metal from 
any new mines, such as was poured upon the world’s market 
from the almost simultaneously-discovered surface ores of Mon- 
tana and Arizona, and the cupriferous pyrites of the Iberian 
peninsula. 

The Lake Superior mines seem to offer the greatest probabil¬ 
ity of' a future important increase in copper-production, and this 
is fortunate indeed, considering the enormous expansion of elec¬ 
trical interests, and the value of this especial copper for that pur¬ 
pose. 

At the first glance, this fact may not be so obvious, especially 
when we see the great depth already reached by the only impor¬ 
tant mines in that section, and the knowledge we possess of the 
limitation longitudinally of the ore-chutes on which they depend 
for their entire product. 

But, as Mr. Douglas points out, the Keweenaw rocks extend 
beyond Michigan and Wisconsin, way through into Minnesota, 
where they are still copper-bearing, though, so far as yet known, 
to a very limited extent. But their out-crop is so heavily covered 
through much of their course by swamp and alluvium, that but 
little is known of their real value, and it is rather probable than 
otherwise, that where the theater of action remains the same, 
as evinced by the identity of the geological formation, the pe¬ 
culiar conditions that have produced a Calumet & Hecla or a 
Quincy, may be repeated many times. 

And it is well known that in Michigan itself, there is an 
almost boundless area of low-grade conglomerates and amygda- 
loids carrying one-half per cent, of copper or thereabouts, and 
thus approaching the standard that the Atlantic mine actually 
finds profitable. So that a slight increase in the price of copper 


28 MODERN AMERICAN METHODS OF COPPER SMELTING. 

would probably render profitable a tract of country extensive- 
enough to supply the world for a long period. 

Therefore there need be no fear of a dearth of copper at 
reasonable prices for more than one generation to come, while, 
on the other hand, there is little reason to expect any sudden im¬ 
portant increase in the production of this most important metal. 


CHAPTER III. 


METHODS OF COPPER ASSAYING. 

The first step usually taken in the treatment of an ore of cop¬ 
per is to learn its value by determining the proportion of that 
metal that it contains. This process is called assaying, as distin¬ 
guished from chemical analysis, which includes the further in¬ 
vestigation as to the general composition of the ore. 

We shall confine our discussion in this place to assaying only. 
The assaying of any given parcel of ore is necessarily pre¬ 
ceded by the process of sampling , by which we seek to obtain, 
within the compass of a few ounces, a correct representative of 
the entire quantity of ore, which may vary in amount from a 
few pounds to several thousand tons. As a ride, it will lessen 
the chance of serious error in very large transactions, to divide 
the lot into parcels of not over fifty tons each, and sample each 

of these lots by itself. 

•/ 

The utmost care and vigilance in sampling and assaying 
should be required at every smelting-works, both in the interest 
of the works and in that of the ore-seller. 

Until quite recently, it has been customary to sample lots of 
ore by quartering them down, rejecting a certain proportional 
part at each successive operation, and reducing the size of the 
ore fragments as the quantity to operate on diminishes. This is. 
a laborious and expensive method, and in the case of finely pul¬ 
verized ores, may well be replaced by the use of the “split 
shovel/’ or one of the many automatic sampling machines that 
have been invented. 

But since the establishment of public sampling works at most 
of our great mining centers, where the correctness of the sample 
is guaranteed by the works, which distribute packages of each lot 
of ore to the agents of the various rival smelting companies, for 
them to assay and bid upon, the vast quantities of ores handled, 
and the importance in many instances of retaining the lump form 


30 MODERN AMERICAN METHODS OF COPPER SMELTING. 


of the ore, as essential to the subsequent metallurgical operations, 
have imperatively demanded some method of automatic sampling 


that shall be rapid, accurate, and equally applicable to ores in 
both the pulverized and lump form. 

The means hitherto employed all depend upon the same gen¬ 
eral principle of cutting or dividing a falling stream of ore by 
means of flanges, fingers, or traveling buckets, in such a manner 


as to obtain a certain desired proportion of it for a sample. 

While many of these devices work admirably upon pulverized 
ore, free from dampness or foreign obstructing substances, they 
are apt to give entirely unsatisfactory results upon a mixture of 
fine and coarse ores, while the presence of strings, chips, rags, 
etc., usually clogs them and deranges their working. 

Mr. D. W. Brunton, of Denver, Colorado, whose paper I have 
freely used, has invented an automatic sampling-machine that is 
apparently free from all the defects enumerated, and which has 
been shown by practical trial to be equally applicable to coarse, 
fine, or mixed ores, while it cannot be clogged by foreign bodies 
of any reasonable size.* 

Brunton overcomes these difficulties by deflecting the entire 
ore-stream to the right or left, while falling through a vertical or 
inclined spout. By a simple arrangement of movable pegs, in 
connection with the driving gear, the proportion of the ore-stream 
thus deflected into the sample-bin may vary from 10 to 50 per 
cent.; the latter amount only being required in coarse ores of 
enormous and very variable richness, while for ordinary lump 
ores, from 10 to 20 per cent, is the maximum required. 

Instead of passing the sample-stream of ore into a bin, this 
system may be still further perfected by leading it directly to a 
pair of moderately fine rolls, the product of which is elevated to 
a second similar sampling-machine, from which the final sample 
drops into a locked bin. 

Six months’ constant experience with this sampler has shown 
that 10 per cent, of 20 per cent., or 2 per cent, of the original ore- 
parcel, is usually quite sufficient; though in exceptional cases, 15 
per cent, of 30 per cent., or 4 h per cent, of the ore, may be re¬ 
quired. 


* See Transactions of the American Institute of Mining Engineers , Yol. 
;<iii.. page 639, for drawings and full description of this sampler. 



METHODS OF COPPER ASSAYING 


31 


The two machines are driven at different speeds, to prevent 
an\ possible error that might arise from isochronal motion, and 
by careful tests of this machine in resampling lots of ore, the 
limit of error has been found less than one-fourth of one per 
cent.; while even the best hand-sampling may vary two per cent. 

The fact that the division is one of time and not of ore is one 
of the most important features of this valuable invention, as it 
consequently is forced to deflect the exact proportion of the ore- 



stream for which it is set • whether coarse or fine, wet or dry, 
light or heavy. A still more recent invention of Mr. Brunton’s, 
is the quartering shovel, described in the Engineering and Mini tig 
Journal of June, 1891. 

The determination of the moisture present in any given par¬ 
cel of ore is also a matter of much importance; and probably 
more inaccuracies attend this apparently simple process than any 
other of the preliminary operations. 






















































































32 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


This determination must, of course, take place as nearly as 
possible at the same time that the entire ore parcel is weighed, 
as otherwise the sample may lose or gain moisture. 

In lump ores, it is difficult to obtain a correct sample, even 
for moisture, without some preliminary crushing, and to save 
labor, it is best to use a portion of the regular assay sample for 
this purpose 5 the accurate weighing of the entire ore parcel being 
postponed until just before or after the sampling, and the por¬ 
tion reserved for the moisture determination being placed in an 
open tin vessel, contained in a covered metal case, having an inch 
or two of water 011 its bottom, in which the sample tins stand. 

From one-fourth to one-half pound of the sample is usually 
weighed out for this determination, and dried under frequent 
stirring, and at a temperature not exceeding 212 degrees. While 



BRUNTON’S QUARTERING SHOVEL. 


it is always important to keep within the limit of temperature 
just mentioned, it is especially the case with certain substances 
which oxidize easily. Among these are finely divided sul¬ 
phides, and above all, the pulverulent copper cements obtained 
from precipitating copper with metallic iron from a sulphate 
solution. 

Such a sample, containing actually per cent, of moisture, 
showed an increase of weight of some 2 per cent, on being ex¬ 
posed for thirty minutes to a temperature of about 235 degrees 
Fahr. 

Certain samples of ore—especially from the roasting furnace 
—are quite hygroscopic, and attract water rapidly after drying. 

In such cases, the precautions used in analytical work must 
be employed, and the covered sample weighed rapidly, in an at¬ 
mosphere kept dry by the use of strong sulphuric acid. 

The sampling of the malleable products of smelting, such as 
blister copper, metallic bottoms, ingots, etc., can only be satisfac- 





METHODS OF COPPER ASSAYING. 


33 


torily effected by boring a hole deeply into a certain proportional 
number of the pieces to be sampled. 

Where snch work is only exceptional, an ordinary ratchet 


hand-drill will answer, but in most cases, a half-inch drill run by 
machinery is employed. 

The chips and drillings are still further subdivided by scissors, 
and as even then it is difficult to obtain an absolutely perfect 
mixture, it is best to weigh out and dissolve a much larger 
amount than is usually taken for assay, taking a certahi pro¬ 
portion of the thoroughly mixed solution for the final deter¬ 
mination. 

The various means employed in the laboratory for the deter¬ 
mination of the percentage of copper in any substance are given 
in the standard works so fully and clearly, that a mere enumera¬ 
tion of the four methods that the author deems necessary and 
sufficient for the assay department of any copper works would 
probably suffice. But having been at considerable pains in for¬ 
mer years to determine the causes and extent of the inaccuracies 
inseparable from certain of these methods, and also having no¬ 
ticed various essential precautions, not mentioned in the text¬ 
books on this subject, the author has introduced a few original 
observations where they seem required. 

The four methods of assay that are quite sufficient for any 

commercial or technical laboratory, and yet that are every one 

essential if it be desired to fulfill every condition to the best ad- 

«/ 

vantage, are: 


I. Titration with potassium cyanide (KCy). 

II. Precipitation with zinc (or iron). 

III. Colorimetric determination. 

IV. Electrolytic. 

*/ 

To these may be properly added the Lake Superior fire assay, 
as peculiarly suited to its local conditions. As the Swansea fire 
assay for copper is described in every English metallurgical work, 
and as the reasons for its adoption in this country can hardly be 
imagined, it is omitted. 


I. TITRATION WITH POTASSIUM CYANIDE. 

This well-known and rapid method, usually called “ The 
Cyanide Assay,” depends upon the power possessed by an aque- 


34 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


ous solution of potassium cyanide to decolorize an ammoniacal 
solution of a copper salt, and is, under proper conditions, quite 
accurate enough for ordinary purposes. These conditions are as 
follows: 

The use of measured and constant amounts of acid and am¬ 
monia. 

The cooling of the ammoniacal copper solution to nearly the 
temperature of the surrounding atmosphere before titration. 

The intimate mixture of the cyanide solution, as it drops from 
the burette, with the copper solution, and a sufficient, though 
accurately limited, time in which to accomplish its bleaching 
action. 


The establishment of a certain fixed shade of pink at the 
standardizing of the cyanide solution, to which all subsequent 
assays must be as closely as possible approximated in color for 
the finishing point. This renders it impossible for any chemist 
to work with another person’s solution until he has first standard¬ 
ized it himself, and determined its strength according to his own 


custom. 

The absence of zinc, arsenic, and antimony, whose presence 
has long been known to seriously vitiate results, though exactly 
to what extent has never been demonstrated, until a series of 
experiments on this point was carried out in 1882 under the 
direction of the author, and still more recently by Torrey & 
Eaton. 

From a long list of results, some of them even contradictory, 
the following deductions were drawn: 

The presence of zinc in quantities below 44 per cent, has no 
perceptible influence on results. 

Five per cent, of zinc, in a siliceous ore of copper, containing 
no other metals except iron, caused a constant error on the plus 
side of about 0*22 per cent., which increased in a tolerably regu¬ 
lar ratio with an increased percentage of zinc. 

After eliminating a few results that varied very greatly and 
unaccountably from all others, an average of about six determi¬ 
nations of each sample yielded the following figures. The ore 
just described was used in every case, and the zinc added in the 
shape of a carefully determined sulphide, allowances being also 
made for the increase in the weight of the ore sample resulting 
from this addition of foreign matter 


METHODS OF COPPER ASSAYING. 


35 


Ore free from 

zinc, 


11*16 

per cent, copper. 

No. 1 with 

4 

per cent. 

zinc, 

11*46 

i i 

u 

4 4 O 

Li 

44 

4^ “ 

44 

11*55 

ti 

n 

“ 3 

44 

5 

44 

44 

11*72 

ll 

ll 

“ 4 

44 

G 

44 

44 

12*1 

u 

a 

“ 5 

u 

8 

u 

44 

13*2 

a 

u 

“ 6 

u 

10 

4 4 

4 4 

13*3 

u 

a 

“ 7 

u 

15 

4 4 

44 

13*9 

n 

ll 

“ 8 

u 

20 

44 

44 

13*8 

u 

a 


The presence of arsenic and antimony in mncli smaller pro¬ 
portions—1 per cent, or less—may cause errors on both plus and 
minus sides to the extent of one-half a per cent, or more, and in 
larger quantities will generally render the test totally unreliable. 

Another indispensable and oft-neglected precaution is the test¬ 
ing of the precipitate of hydrated oxide of iron caused by the 
addition of ammonia to the original solution. This bulky precipi¬ 
tate, especially in the case of mattes and highly ferruginous ores, 
will retain a considerable amount of copper which even the most 
careful washing will not remove, but winch may be speedily deter¬ 
mined by dissolving the precipitate in the smallest possible 
quantity of muriatic acid, saturating with ammonia, and again 
titrating if any blue coloration is produced. The following re¬ 
sults, taken from the note-book of an experienced chemist, who 
had never been aware of this possible source of error until acci¬ 
dentally mentioned to him by an assayer in the employ of the 
writer, and who at once instituted careful experiments to ascer¬ 
tain the probable extent of the mistakes that he had made while 
acting as assayer to large smelting-works, give some idea of the 
serious discrepancies that may arise from the non-observance of 
this precaution: 

Without resolution of With resolution of 

Character of sample. precipitate. precipitate. 


No. 

1, pyritous ore. 

21*2 

per cent, copper 

23*7 

per cent, copper 

44 

2, bornite. 

. 37*8 

44 

a 

42*4 

a 

44 

4 4 

3, cupola matte. 

. 27*7 

u 

a 

31*2 

a 

a 

a 

4, reverberatory matte.. 

.. 46*4 

44 

a 

47*4 

a 

a 

a 

5, blue metal. 


a 

44 

58*2 

a 

a 

u 

6, white metal. 

. 74*7 

a 

a 

75*2 

a 

a 

44 

7, regule. 

. 86*2 

44 

44 

86*4 

a 

a 

ii 

8, blister copper. 

. 97*3 

44 

a 

97*2 

a 

a 


As might be expected, the greatest discrepancies exist in con¬ 
nection with those samples containing the largest amounts of iron, 
and decrease to nothing as the iron contents diminish. 









36 MODERN AMERICAN METHODS OF COPPER SMELTING. 


In the absence of the injurious elements—zinc, arsenic, anti¬ 
mony—the cyanide assay is sufficiently accurate, and, from its 
.simplicity and rapidity of execution, it is peculiarly adapted to 
the daily working assays from the mine, smelter, and concentra¬ 
tor. In fact, it is the mainstay of the overcrowded metallurgical 
assayer, and can be used for nearly every purpose, except for the 
buying and selling of ores and copper products, and for the de¬ 
termination of very minute quantities of copper in slags. It is 
frequently employed with satisfaction for the last-named purpose, 
a much larger amount than usual being taken, in order to obtain 
a solution sufficiently rich in copper to exhibit a reasonable de¬ 
gree of color. Messrs. Torrey & Eaton have published addi¬ 
tional investigations of great value on the effect of various sub¬ 
stances upon the accuracy of the cyanide method. (See Engineer¬ 
ing and Mining Journal , May 9th, 1885.) 

In their experiments, they employed a cyanide solution capa¬ 
ble of showing one-thirtieth of one per cent, of copper, and took 
every precaution to have all conditions identical during the vari¬ 
ous tests; all solutions titrated being of the same degree of 
strength. 

Silver and Bismuth .—-A solution was made of the following 
metals: 

Copper.-550 gram. 

Bismuth.'200 “ 

Silver.-250 “ 

The silver was precipitated with hydrochloric acid, and am¬ 
monia added after filtering and washing. Two titrations gave : 


No. 1.54'90 per cent, copper 

No. 2.54'85 u u instead of 55 per cent. 


These results show that a solution containing the very un¬ 
usual proportion of 20 per cent, of bismuth and 25 per cent, of 
silver can be titrated to within 0T per cent, of its value in copper. 

Lead .—This metal, being a common element in copper ores 
and alloys, was introduced into a copper solution in the following 
proportions: 

Copper...-200 gram. 

Lead.-800 “ 

After adding ammonia and allowing the lead precipitate to 
.separate for two or three hours, it was titrated, giving 20‘28 per 









METHODS OF COPPER ASSAYING. 


37 


cent, of copper, instead of 20 per cent. Messrs. Torrey & Eaton, 
therefore, believe that the amount of lead commonly present in 
ores—from 5 to 40 per cent.—woidd not injuriously affect the 
operation. 

Arsenic .—Torrey & Eaton titrated, without filtering, a solu¬ 
tion containing '600 gram arsenic, '400 gram copper, finding 39'8 
per cent, instead of 40 per cent. Therefore any ordinary amount 
of arsenic—from 5 to 15 per cent.—would seem to have no in¬ 
jurious influence. 

Ammonia and hydrochloric acid, when indiscriminately used, 
were found by Messrs. Torrey & Eaton to cause serious errors, 
the results being influenced to the extent of from 4 to 1 per cent, 
by any large excess of either. 

Lime in large quantity was found to confuse results. 

Magnesia had no effect whatever. 

II. PRECIPITATION WITH ZINC. 

This is simply a modification of the well-known Swedish 
method, and has been so arranged by Kerl (see his work on as¬ 
saying) as to be suitable for every variety of ore or product, re¬ 
gardless of impurities. In fact, its chief value in the modern 
metallurgical laboratory is to take the place of the cyanide 
method in those cases in which the occurrence of deleterious sub¬ 
stances forbids the employment of the latter. 

The principal drawback to this method of assay is the delay 
caused by the precipitation, and the drying and weighing of this 
precipitate, whose strong hygroscopic quality renders the latter 
manipulation tedious and frequently inaccurate. This can be 
easily obviated by dissolving this precipitate, now free from all 
impurities, and determining the percentage of copper by the ordi¬ 
nary cyanide assay. This modification can be strongly recom¬ 
mended. 

III. THE COLORIMETRIC DETERMINATION OF COPPER. 

This is reserved almost exclusively for the determination of 
minute quantities of copper contained in slags, tailings from con¬ 
centration, and similar products. 

Heine’s modification of this method, as described by Kerl, is 
perhaps the most convenient, and with proper solutions for com¬ 
parison, preserved in bottles of colorless glass and of exactly the 


38 MODERN AMERICAN METHODS OF COPPER SMELTING. 


same size, yields results that cannot be surpassed. It is seldom 
employed for substances containing over one and one-half per 
cent, of copper, and may be relied upon to show differences of 
T fo- of one per cent.; results, however, depending largely upon 
the skill of the operator, and his capacity for discriminating al¬ 
most invisible shades of color. 


IV. THE ELECTROLYTIC METHOD, OR BATTERY ASSAY. 

This is suited to nearly every class of material and every per¬ 
centage of copper, from the highest to the lowest, and owing to 
its ease of execution and extreme accuracy, has already largely 
supplanted the ordinary analytic methods, and bids fail* to do so 
altogether in all important cases. Among those assayers who do 
not yet practice it, there seems to be an impression that it is 
difficult of execution, and in several cases under the author’s ob¬ 
servation it has been abandoned after a few futile efforts. In 
these instances there must have been some direct violation of the 
laws governing the generation and transmission of electricity—it 
being always the battery that was complained of—and as a simi¬ 
lar though usually much more extensive and complicated form 
of battery is under the charge of every telegraph operator, the 
disappointed assayer should feel encouraged to persist. 

Messrs. Torrey & Eaton have also investigated the effect of 
various substances upon the battery assay, and have arrived at 
the following results, which are not quite so favorable as the au¬ 
thor’s experience in practice has been : * 

u Silver, when present in any considerable proportion—from 1 
to 3 per cent.—gives too high a result. It should always be re¬ 
moved bY hydrochloric acid. 

u Bismuth, even when present in small quantity—f per cent. 
—is partly or wholly precipitated with the copper, and must con¬ 
sequently be determined analytically in the deposit. A solution 
of ‘970 gram copper, '030 gram bismuth, gave 97*9 per cent, cop¬ 
per instead of 97 per cent. 

“Lead, derived from the resolution of sulphate of lead (if pres¬ 
ent) by the wash-water, is partially precipitated with the copper. 
This applies only to large percentages of lead. 


* Mr. Sperry’s experience shows that with proper precautions, these 
unfavorable results may be completely avoided. 



METHODS OF COPPER ASSAYING. 


39 


"Zinc and Nickel do not interfere in quantities up to 30 per 
cent. 

“Arsenic precipitates partly with the copper, and not after it, 
as has been supposed. It gives a bright deposit, but may be 
found in considerable quantity in the precipitate, before the so¬ 
lution is tree from copper. After complete precipitation of the 
copper, therefore, the deposit should be titrated with cyanide of 
potassium.” 

Feeling that the important part played by the battery assay 
in modern copper metallurgy calls for a more detailed and per¬ 
fect description than can be given by one whose assaying days 
are long past, I turned naturally to a chemist whose daily work 
lay in that direction, and was fortunate in securing the aid of Mr. 
Francis L. Sperry, analytical chemist, and for five years chemist 
to the Canadian Copper Company at Sudbury, Ontario. 

The following description of the battery assay must therefore 
be credited to Mr. Sperry. 

The notes on the electrolytic determination of copper are made 
up from the experience of five years’ constant use of the method. 

The scheme, as given, is intended to present the details in as 
practical and concise a manner as possible without going beyond 
the province of this work. Those who desire to study more 
closely the electrolysis of other metals, and also the treat¬ 
ment of copper in oxalate solutions which can advantageously 
be made use of, are referred to the admirable work of Dr. Classen 
on “ Quantitative Chemical Analysis by Electrolysis,” and also 
u Electro-Chemical Analysis,” by Professor Edgar F. Smith. 

THE DETERMINATION OF COPPER BY ELECTROLYSIS. 

Of the various methods the chemist has in hand for the de¬ 
termination of copper, the electrolytic method presents some ad¬ 
vantages over other recognized forms. It permits of reliable, 
clean, and rapid work, and enables the chemist to remove copper 
from a solution completely, in the presence of other metals, which 
may subsequently be determined in the same solution. 

The requirements are clean platinum cathodes and anodes 
and a uniform current of electricity of known strength. 

Take, for a weighed sample, one-half a gram copper matte, 
one or two grams copper ore, depending on the richness of the 
ore, and two or three grams for slag. 


40 MODERN AMERICAN METHODS OF COPPER SMELTING. 


In preparing the samples they should he sifted through an 
eighty-mesh sieve. Weigh out on an accurate chemical balance. 

After weighing the samples in duplicate, on watch glasses, 
transfer carefully to No. 2 beakers, slightly moisten with cold 
distilled water, add twenty-five c. c. strong nitric acid and ten 
to fifteen drops of strong sulphuric acid. The beakers should be 
covered with watch glasses and set on the sand bath, where they 
are heated until the nitrous acid fumes have all passed off and 
the sample is in solution. Wash the watch glasses down into 
the beaker, and evaporate the solution to dryness. 

When choking white fumes appear, set the beakers one side 
to cool. The copper is now in the form of sulphate. Moisten 
the mass in the beakers with dilute nitric acid (1‘20'sp. gr.), 
using about six or seven c. c.; add four drops of sulphuric acid, 
forty c. c. of water, and heat on sand bath until the mass is in 
solution. Filter off the insoluble matter (which should be exam¬ 
ined to see if there may be copper left in the residue, undis¬ 
solved), reserving the filtrate in a No. 1 beaker. The solution is 
now ready to be electrolyzed. 

The electrical energy necessary to electrolyze a copper solution 
is furnished by various batteries of reliable manufacture. If 
there is an electric light plant at hand the wire, properly insu¬ 
lated, can be run through the laboratory, and by means of a re¬ 
sistance coil the current can be reduced in strength sufficiently 
to permit of quantitative electrolytic determinations. The (Ire- 
net, Gravity, or Grove cell batteries will be found well adapted 
for generating the necessary strength of current also. The Gre- 
net cell loses its intensity after long use. The Gravity cell is very 
likely to act unsatisfactorily on account of local action setting in, 
causing polarization of the electrodes, and the electrical energy 
ceasing entirely. The Grove cell requires more care than either 
of the others spoken of, but the electromotive force is certain to 
act for as long a time as is necessary for the deposition of the 
metal, as the copper solutions are set on the battery at night and 
removed on the following morning, usually. 

It is best to have a surplus of electrical energy for the elec¬ 
trolysis, although too strong a current must be guarded against. 

Three Grove cells, freshly made up, will furnish current 
sufficient to electrolyze six to eight copper solutions, none of 
which contain more than '5 gram copper in 1 gram of sample. 


METHODS OF COPPER ASSAYING. 


41 


Four cells will electrolyze eight to ten solutions, and five cells 
ten to twelve solutions. 

A convenient arrangement for supporting the cathodes and 
anodes for as many as twelve simultaneous determinations of cop¬ 
per is shown by the illustration (Fig. I.). 

The rods are § inch square by 39 inches long. Holes for the 
insertion of anode and cathode rods are 3J inches apart and ^ 
inch in size, while through the side of the brass rods a milled 
screw sets against a flexible brass shoe, which binds the cathode 



FIG. I.—RACK FOR BATTERY ASSAY. 


and anode platinum rods securely in position. The brass rods, 
J inch apart, are supported on glass pillars, and can be raised or 
lowered as required. 

The most convenient form of cathode is a plain platinum 
cylinder 2.J inches long, 1 inch diameter, and the rod that sup¬ 
ports it is 4^ inches long. It weighs about 16 to 18 grams. 
(Fig. II.) 

These cathodes may seem large, but for general class of work 
on high and low grade copper ores and mattes they will be found 
a very convenient size, as they offer a large surface for the depo¬ 
sition of copper, whereas, if they were smaller, frequently the 
copper would be deposited in spongy form, and there would be 
loss in weighing. 
































































42 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


The anodes are platinum wire of size to fit T V inch hole, made 
in the form of a concentric circle, from the center of which the 
rod stands out 7 inches. (Fig. III.) 

The diameter of the coil is 1 inch. By this arrangement of 
the anode there is a uniform evolution of gas throughout the so¬ 
lution, and the inside as well as the outside of the cathode is 
evenly electroplated with copper. 

The cathode should not be completely immersed in the solu¬ 
tion to be electrolyzed. When it is supposed that all the copper 
is deposited, immerse the cathode deeper in the solution and let 
the current run one-lialf hour longer. Any deposition on the 
clean surface will show at once that copper remains still in the 
solution. If the copper is all deposited, loosen the anode and 

CATHODE ANODE 



FIG. II. FIG. III. FIG. IV. 

carefully remove it and the beaker. Wash the cathode quickly 

«/ -i- «/ 

into a clean No. 3 beaker with distilled water, immerse in pure 
alcohol, and gently ignite in flame until dry. The copper should 
be a pink rose color. Weigh as soon as cooled to the tempera¬ 
ture of the room. 

The current should not lie passed through the solution 
longer than is necessary to effect the complete deposition of 
the copper, as secondary reactions are liable to set in. 

When there has been a separation of copper in a nitric 
acid solution alone, the solution should be siphoned off into a 
clean beaker without interrupting the current, and the cathode 
washed with pure water, otherwise the nitric acid will dissolve 
some of the deposited copper into the solution again. Too 














METHODS OF COPPER ASSAYING. 


43 


much nitric acid will keep the copper in solution. Too much 
sulphuric acid will cause the copper to deposit in spongy form. 

Too strong a current will cause loss by too great evolution of 
oxy-liydrogen gas, the copper will deposit dark colored, and if 
zinc is present it will deposit on the copper. 

By using deep beakers (Fig. IV.), there will be scarcely a per¬ 
ceptible loss of solution by the evolution of gas, as the sides of 
the beaker should be carefully washed down half an hour before 
removing the cathode to weigh. 

The secondary reactions to be guarded against in passing the 
current longer than is necessary to deposit the copper, and also 
in not having the solution of proper strength of acid, are the con¬ 
version of the nitric acid into ammonia and the formation of am¬ 
monia sulphate, so that if the deposition of coppei* were done in 
the presence of iron and zinc, these metals would be deposited on 
the cathode as hydrated oxides. 

With the conditions described above conformed to, copper is 
completely deposited and removed from solutions containing iron, 
alumina, manganese, zinc, nickel, cobalt, chromium, cadmium, 
lime, barium, strontium, and magnesium. 

In the laboratory of the writer it has been customary to make 
electrolytic separations of copper and nickel daily for the past 
five years, and in every case with unvarying accuracy. The cop¬ 
per was removed completely in the presence of nickel, iron, and 
zinc, and these elements subsequently determined in the same so¬ 
lution. 

Examples could be given ad infinitum , but a few will be given 
of the most characteristic. 


Slag 


f 1 gm- 

I Copper, 
l Nickel, 


Sample taken. 
1 2 


0 - 42 % 0 - 42 % 

0 - 41 % 0 - 40 °/ 


Copper Ore 


' 1 gm. 

Copper, 

^Nickel, 


Sample taken. 
1 2 


8 - 44 % 8 - 43 % 

3 - 33 % 3 * 35 % 


Nickel Ore 


' 1 gm. 

Copper, 
. Nickel, 


Sample taken. 
1 2 


1 - 23 % 1 - 24 % 

8 - 62 % 8 ’ 63 % 









44 310DERN AMERICAN METHODS OF COPPER SMELTING. 


Copper Matte 


| .5 gm. 

Copper, 

.Nickel, 


Sample taken. 

1 2 

33 - 45 % 33 - 46 % 

15 - 75 % 15 - 73 % 


Nickel Matte 


" .5 gm. 

1 Copper, 
.Nickel, 


Sample taken. 

1 2 

16 - 76 % 16 - 78 % 

21 - 23 % 21 - 25 % 


In each case the nickel was determined electrolytically in the 
same solution from which the copper was removed. 

By carefully noting what are the best conditions, as there is 
a certain limit within which variation in the. treatment of mis¬ 
cellaneous samples is warranted, most any novice will find elec¬ 
trolysis a simple and accurate method for the estimation of cop¬ 
per. 







CHAPTER IV. 


THE ROASTING OF GOPPER ORES IN LUMP FORM.* 

Roasting or calcination, used indiscriminately in the lan¬ 
guage of the American copper smelter, signifies the exposure of 
ores of metals containing sulphur, arsenic, and other metalloids 
to a comparatively moderate temperature, with the purpose of 
effecting certain chemical, and rarely mechanical, changes re¬ 
quired for their subsequent treatment. This definition is re¬ 
stricted to the dry metallurgy of copper, and does not take into 
consideration chloridizing roasting, roasting with sulphate of 
soda, and other well-known variations, which belong either to 
the metallurgy of the precious metals or to the wet treatment of 
copper ores. 

The care and attention which should be devoted to this pre¬ 
paratory process cannot be too strongly insisted on, nor can any 
one carry out either this apparently simple roasting or the follow¬ 
ing fusion to the best advantage, who is not thoroughly familiar 
with the striking chemical changes that in every calcination fol¬ 
low closely upon each other, and by which the sulphides and ar¬ 
senides of the metals are transformed at will into a succession of 
subsulphides, sulphates, subsulphates, and oxides. These, react¬ 
ing upon each other according to fixed and well-known laws, en 
able the metallurgist at his pleasure to produce every grade of 
metal from black copper to a low-grade matte that shall contain 
nearly all the metallic contents of the ore in combination with 
sulphur. To avoid constant repetition, it may be understood that 
in speaking of calcination, when sulphur is mentioned, its more 
or less constant satellites, arsenic and antimony, are also included, 

their behavior being somewhat similar under ordinary circum- 
■ ■ * ~ 

* In English metallurgical literature, the term roasting is applied exclu¬ 
sively to that process in which copper matte in large fragments is exposed on 
the hearth of a reverberatory furnace to an oxidizing atmosphere, and a mod¬ 
erate, but gradually increasing temperature. See “ Matte Concentration.” 





4G MODERN AMERICAN METHODS OF COPPER SMELTING. 


stances. These very different products, as well as the amount of 
ferrous oxide, the most important basic element of every copper 
slag, result solely from the degree to which the calcination is car¬ 
ried. In fact, it may be taken as literally true, that the compo¬ 
sition of both the valuable and waste products of the fusion of 
any sulphide ore of copper is determined irrevocably and entirely 
in the roasting-furnace or stall. A more thorough study of the 
reactions just referred to will be found in its proper place. 
Enough has here been said not only to explain the author’s object 
in devoting so much attention to this process, but also to induce 
such metallurgists as are not already thoroughly familiar with 
the theory of calcination to endeavor to become so if they desire 
to ever excel in the economical treatment of sulphide ores. 

The varieties of calcination, as applied to the dry treatment 
of copper ores, are at most two : 

1. The oxidizing roasting, which is necessarily combined with 
volatilization. 

2. The reducing roasting, limited in its application almost ex¬ 
clusively to substances containing much antimony or arsenic. 

Planner’s admirable work on Rostprocesse contains the whole 
theoretical part of calcination ; but a foreign language is a bar¬ 
rier to many ardent students of metallurgy, and his descriptions 
and plans of furnaces and apparatus apply to those in use dim¬ 
ing the past generation. A modern treatise on roasting, regard¬ 
ing the subject principally from a practical standpoint, and 
adapted to present American conditions, seems desirable. Such 
a treatise, however, could not attain the highest degree of useful¬ 
ness without a consideration of the theory of calcination sufficient 
to enable and encourage all who make use of the more practical 
part to follow with ease the chemical reactions on which the pro¬ 
cess is based. These reactions can be more easily appreciated 
and remembered after first becoming familiar with the apparatus 
and means by which the exposure of the substances under treat¬ 
ment to the influence of heat and air is effected. The theoretical 
discussion will be postponed until this familiarity is attained. 

This roasting apparatus must vary according to the mechan¬ 
ical condition of the ore under treatment—that is, whether fine or 
coarse. (See article by the author, u The Roasting of Copper Ores 
and Furnace Products.” United States Geological Surrey, Mineral 
Resources of the United States, Albert Williams, Jr., 1883.) It is 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


47 


assumed that the process of calcination, as executed in the dry 
metallurgy of copper, has to deal with the oxidizing of only two 
classes of material, ores and mattes. The appliances for the 
roasting of these substances in lump form may be divided into 
three classes: 

1. Heap roasting. Suited to both ore and matte. 

2. Stall roasting: 

a. Open stalls. Suited only to ore. 

1). Covered stalls. Suited to both ore and matte. 

3. Kilns. Suited only to ore. 

•/ 

The mechanical preparation of the material for each of these 
three forms of roasting is virtually identical, and has an impor¬ 
tant influence on the result of the process. The size to which the 
substance under treatment should lie broken cannot be arbi¬ 
trarily stated, as different ores vary so greatly in their composi¬ 
tion and behavior. Ores containing a high percentage of sulphur 
—twenty-five and over—will give excellent results if so broken 
that the largest fragments shall be capable of passing through a 
ring three inches in diameter; while more rocky ore, which is 
likely to be of a harder and denser texture, should be reduced to 
pass a two-inch opening. Careful experiments can alone deter¬ 
mine the most profitable size for any given material, and should 
be continued on a large scale until the metallurgist in charge has 
fully satisfied himself on this point. This may be determined 
with the least trouble and expense by noticing the weight and 
quality of the matte obtained by smelting the roasted ore from 
various heaps formed of fragments differing in their maximum 
size. 

All other conditions being identical, the heap that yields the 
smallest quantity of the richest matte has, of course, undergone 
the most perfect oxidation, and should be selected as a standard 
for future operations. Variations that may occur in the chem¬ 
ical or mechanical condition of the ore should be carefully 
watched as a guide in fixing upon the best roasting size. Local 
conditions must determine whether a jaw-crusher or hand labor 
should be used for this purpose. The production of fines is a de¬ 
cided evil in the preparation of ore for heap roasting, and the 
manual method possesses a certain advantage in this respect, 
though this consideration may be outweighed by other economic 
conditions. A trial of the comparative amount of fines produced 


48 MODERN AMERICAN METHODS OF COPPER SMELTING. 


by machine and hand-breaking was carried out on three different 
varieties of sulphnreted copper ores of average hardness, and ag¬ 
gregating 2,220 tons* The broken ore was thoroughly screened; 
all passing through a sieve of three meshes to the inch (6 mm. 
openings) was designated as fines.t One-half (1,110 tons) of this 
material was passed through a seven by ten jaw rock-breaker, 
with corrugated crushing-plates (which produce a decidedly less 
proportion of fines than the smooth plates). The breaker made 
240 revolutions per minute, and had a discharge opening of two 
and one-half inches. The other moiety was broken by experi¬ 
enced workmen, with proper spalling-hammers, into fragments 
of a similar maximum size. The result was as follows, only the 
fine product being weighed, the coarse being estimated by sub¬ 
tracting the former from the total amount: 


Broken by Jaw-Cruslier. 

Fine product—below 6 mm. in diameter. 

Coarse product—between G mm. and 64 mm. 

Total. 


Broken by Hand Hammers. 

Fine product—below 6 mm. in diameter. 

Coarse product—between 6 mm. and 64 mm. 

Total. 


Tons. Per cent 
192-25 17-32 

917-75 82-68 


1,110-00 100-00 


103-34 9-31 

1,006-66 90-69 

1 , 110-00 100-00 


These results are quite in accordance with impressions derived 
from general observation, and, as will be noticed, prove that, with 
certain classes of ore, mechanical crushing produces nearly 
double as much fines as hand-spalling. As 10 per cent, of fines is 
an ample allowance to form a covering for any kind of roast-heap 
—and better results are obtained when the same partially oxi¬ 
dized material is used over and over again as a surface protection 
—it may frequently occur that, in spite of its greater cost, hand- 


* Unless otherwise indicated, all tons equal 2,000 pounds, 
t It should also be explained that, owing to the large and very variable 
amount of fine material contained in the ore before crushing, as it came 
from the mine, it was passed over the screen just referred to before being 
either fed to the crusher or spalled by hand. Without this precaution, the 
results of the trial would have been valueless, as the variation in the amount 
of fines in the original ore was far greater than the discrepancy in the- 
amount produced by the two different methods of crushing. 










THE ROASTING OF COPPER ORES IN LUMP FORM. 


49 


spalling may prove more profitable tlian machine-breaking. This 
is a matter for individual decision, and can be determined only 
after a mature consideration of the difference in expense of the 
two operations, the means at hand for the calcination, and sub¬ 
sequent advantageous smelting, of the increased quantity of fines, 
and whatever other factors may bear on the case in hand. The 
following steps should be carried out, whichever method is decided 
upon. The ore, after breaking, should be separated into three 
classes, the largest including all the product between the maxi¬ 
mum size and one inch (25 mm.); the medium size, or ragging, 
consisting of the class between 25 mm. and the fine size (three 
meshes to the inch, which would give openings of about 6 mm. 
net); and the fines, as already explained. Roughly speaking, the 
percentage of each class, including the fine ore that is invariably 
produced during the operation of mining, may be represented by 
the following figures: 

Coarse.55 per cent. 

Ragging...:.25 “ 

Fines.*..20 “ 

Total...100 

This classification is effected with great ease and economy in 
case machine-breaking is decided upon, by the use of a cylin¬ 
drical or conical screen of y\-inch boiler iron, about 8 feet in 
length and 36 inches or more in diameter. This is placed below 
the breaker so that it receives all the ore. It is made to revolve 
from 18 to 22 times per minute, and has a maximum fall of an 
inch to the foot. This can easily separate 10 tons of ore per hour, 
and by proper arrangement of tracks or bins, discharge each class 
into its own bin. One fault in this very simple classifying appara¬ 
tus is, that the coarse lumps of ore must necessarily traverse all the 
finer sizes of screen, thus greatly augmenting the wear and tear. 
This objection, though frequently valid under other circumstances, 
has but little weight when it is remembered that even the small¬ 
est holes (6mm.) are punched in iron of such thickness (fV inch) 
that it will withstand even the roughest usage for many months. 
To produce the three sizes just alluded to, the screen requires 
two sections, with holes respectively 6 mm. and 25 mm., of which 
the finer size should occupy the upper 5 feet, and the coarser the 
lower 3 feet of the screen. In remote districts, where freight is 







50 MODERN AMERICAN METHODS OF COPPER SMELTING. 

one of the principal items of expense, heavy iron wire cloth may 
he substituted for the punched boiler iron, and if properly con¬ 
structed and of sufficiently heavy stock, will be found satisfac¬ 
tory, lasting about one-lialf as long as the more solid material. 
The difference in size between a circular hole 25 mm. in diameter 
and a square with sides of that length, should not be overlooked 
in changing from one variety of screen to the other. The month 
of the crusher should lie level with the feeding-floor, and the lat¬ 
ter should be covered with quarter-inch boiler iron, firmly at¬ 
tached to the planks by countersunk screws, by which arrange¬ 
ment the shoveling is greatly facilitated. With such a plant, two 
good laborers will feed the breaker at the rate of ten tons an 
hour for a ten-hour shift, provided none of the rock is in such 
masses as to require sledging, and that the ore is dumped close 
to the mouth of the breaker. A seven by ten jaw-breaker of the 
best and heaviest make is capable of crushing the amount just 
mentioned to a maximum size of 2h inches, provided the rock is 
brittle, heavy, and not inclined to clog the machine. In most 
cases where this duty is required, and especially if the ore is 
damp and in large fragments, it is much more advantageous to 
substitute a fifteen by nine breaker, which, when geared up to 
230 revolutions and with sufficient power, has a capacity of at least 
twenty tons per hour on favorable ores, and when properly fed. 

The expense per ton of breaking, sizing, and delivering into 
cars with such a plant operating upon ores of medium tenacity, 
is as follows, the figures being deduced from average residts of 
handling fully one hundred thousand tons under the most vary¬ 
ing conditions. It is assumed that the breaker is run by an in¬ 
dependent engine of sufficient power,* while the wages of an en¬ 
gineer and firemen are partially saved by taking the steam from 
the boilers that are supposed to supply the main works: 


* Speaking from a very extensive experience, the author finds that not 
one breaker in ten is run up to anything approaching its capacity, and that 
consequently it has become customary to provide an engine and boiler far 
too small to drive the breaker up to speed when doing full work. The 
statements made above refer to breakers run to their extreme capacity, and 
under these conditions a 7 by 10 crusher requires ,an engine of not less than 
6 by 10 cylinder, while a 15 by 9 crusher requires an 8 by 12 cylinder. As 
each movement of the jaw crushes a given amount of ore, it follows that the 
capacity of a breaker depends upon the speed at which it is run. 



THE ROASTING OF COPPER ORES IN LUMP FORM. 


51 


COST OF BREAKING ORE BY MACHINERY WITH A PLANT OF 100 TONS 

CAPACITY IN TEN HOURS. 

Pouct per day of 10 hours: Per 100 tons. Per ton. 

1,200 pounds of coal at $4.50 per ton. .$2.70 

Oil and lubricants.40 

Engineer, $ wages at $3.75 

Fireman, $ wages at $2.50 $4.35 $0.0435 

Labor: 

Two feeders at $1.75. 3.50 0.0350 

Repairs: 

Toggles and jaw plates, etc.$0.43 

Wear of tools, Babbitt for renewing 

bearings, etc. 0.37 

Daily slight repairs on machinery. 0.35 


Miscellaneous items, sampling, etc.. .. 0.33 

1.48 

0.0148 

Sinking Fund: 



To replace machinery, at 10 per cent. 



on original cost. 

0.78 

0.0078 

Total. 

$10.11 

$0.1011 


If it should seem at first glance that 10 cents per ton is an 
unreasonably low figure, it will be noticed that the cost of trans¬ 
portation both to and from the breaker is not included in this es¬ 
timate ; the former is usually charged to mining expenses, and 
the latter to heap-roasting. Ore that is to undergo roasting in 
kilns for the purpose of acid manufacture must be broken con¬ 
siderably smaller than that just described, and this, of course, 
lessens the capacity of the apparatus and proportionately in¬ 
creases the expense. An increase of 50 per cent, in the above es¬ 
timate will be sufficient to cover it. The figures given above have 
been frequently attained by the author, but only under certain 
favorable conditions, among which are: Abundance of power 
to run the breaker to its full speed, regardless of forced feeding. 
A constant system of supervision by which the plant is kept up 
to its full capacity of ten tons per hour, and which demands ex¬ 
ceptionally good men as feeders. A frequent inspection of the 
machinery, and renewal of all jaw plates, toggles, and other 
wearing parts, before the efficiency of the machine has begun to 
lie impaired ; all of which repairs should be foreseen and executed 
during the night shift or on idle days. A perfect system of 
checking the weight of all ore received and crushed, without 
which precaution a mysterious and surprisingly large deficit will 













MODERN AMERICAN METHODS OF COPPER SMELTING. 


be found to exist on taking stock.* It is hardly necessary to 
mention that all bearings that cannot be reached while the ma¬ 
chinery is in motion must be provided with ample self-oilers, and 
since clouds of dust are generated in this work, that unusual care 
must be taken in covering and protecting all boxes and parts 
subject to injury from this cause. Unless the ore is sufficiently 
damp—either naturally or by artificial sprinkling—to prevent 
this excessive production of dust, the feeders should be required 
to wear some efficient form of respirator; otherwise, they are 
likely to receive serious and permanent injury, the fine particles 
of sulphides being peculiarly irritating to the lungs and entire 
bronchial mucous membrane. 

The breaking of ore by hand hammers , technically denominated 
“ spalling,” is worthy of more careful consideration than is gener¬ 
ally bestowed upon it. The style of hammer is seldom suited to 
the purpose, though both the amount of labor accomplished and 
the personal comfort of the workmen depend more upon the 
weight and shape of this implement and its handle than on any 
other single factor save the quality of the ore itself. There should 
be several cast-steel sledges, differing in weight from G to 14 
pounds, and intended for general use in breaking up the larger 
fragments of rock to a size suitable for the light spalling-ham¬ 
mers. Each laborer should be provided with a hammer G inches 
in length, forged from a 14 inch octagonal bar of the best steel, 
and weighing about 2f pounds. This should be somewhat flat¬ 
tened and expanded at the middle third, to give ample room for 
a handle of sufficient size to prevent frequent breakage. The 
handles usually sold for this purpose are a constant source of an¬ 
noyance and expense, being totally unsuited to this peculiar duty. 
It is better to have the handles made at the works, if it is pos¬ 
sible to procure the proper variety of oak, ash, hickory, or, far 
better than all, a small tree known in New England as iron-wood 
or hornbeam, which, when peeled and used in its green state, ex¬ 
cels any other wood in toughness and elasticity. The handles 

* This is a difficulty that the metallurgist will encounter at every stage 
of his work. In spite of the most accurate scales, and of careful and fre¬ 
quent determinations of weights, the quarterly balance-sheet will invariably 
•show that the actual amount of ore treated is less than the amount shown 
by the weigh-master’s book; while the weights of all supplies consumed, 
especially fuel, have been reported too low. To one unprepared for this 
result, the consequences may be serious. 






THE ROASTING OF COPPER ORES IN LUMP FORM. 


53 

should be perfectly straight, without crook or twist, so that, 
when firmly fastened in the eye of the hammer by an iron wedge, 
the hammer hangs exactly true. Their value and durability de¬ 
pend much upon the skill with which the handles are shaved 
down to an area less than half their maximum size, beginning 
at a point some six inches above the hammer-head and extend¬ 
ing for about ten inches toward the free extremity. If properly 
made and of good material, they may be made so small as to ap¬ 
pear liable to break at the first blow • but in reality they are so 
elastic that they act as a spring, and obviate all disagreeable 
effects of shock; wear longer and do more work than the ordi¬ 
nary handle. Such a handle has lasted five months of constant 
use, in the hands of a careful workman, whereas one of the ordi¬ 
nary make has an average life of scarcely four days, or perhaps 
thirty tons of ore. Where the ore is of pretty uniform charac¬ 
ter, it is advantageous to adopt the contract system for this kind 
of work. A skillful laborer, under ordinary conditions, will 
break seven tons of rock per ten-hour shift to a size of 24 inches,* 
taking coarse and fine as it comes, and in some cases he is also 
able to assist in screening and loading the same into cars. This 
latter operation should be executed with a strong potato-fork hav¬ 
ing such spaces between the tines as to retain the coarsest size, 
while the finer classes are left upon the ground. These forks 
are made for this purpose by a firm in St. Louis, and are much 
superior to the ordinary forks. Adieu a sufficient quantity of 
the finer classes has accumulated and the pile or stall is ready to 
receive its outer layer of ragging, the mixed material should be 
thrown upon a screen inclined to an angle of about 48 degrees 
and having three meshes to the inch. This screen is elevated 
upon legs to such a height that the coarser class that fails to 
pass its openings will be caught in a car or barrow, while the 
fines fall either into a second movable receptacle or upon the 
floor, being in the latter case prevented from again mixing with 
the unscreened ore by a tight boarding on the front and sides of 
the screen frame. The amount of space required for convenient 
spalling is about forty square feet per man, which will allow for 
ore-dumps, tracks, sample boxes, etc. A good light is essential, 

* Unless otherwise specified, the term “day” or “shift” may he under¬ 
stood to signify the ordinary working day of ten hours, from seven a.m. to 
six p.m., with one hour for dinner. 






54 MODERN AMERICAN METHODS OF COPPER SMELTING. 


especially if any sorting is to be done, and it is in this case and 
where fuel is expensive that hand spading frequently presents 
especial advantages. When the ores are siliceous, a mere rejec¬ 
tion of such pieces of barren quartz or wall rock as have accident¬ 
ally got among the ore, or first become visible on breaking up 
the larger masses, may have a most beneficent influence on the 
subsequent fusion. Where the expense of treatment is high and 
work is conducted on a large scale, the profit resulting from rais¬ 
ing the average contents of the ore even a single per cent, is 
hardly credible, even aside from the increased fusibility due to 
the diminished proportion of silica. To illustrate: At certain 
works that the author was called to superintend, it had been the 
custom to spall all the first-class ore just as it came from the 
mine without any sorting out of barren wall rock, considerable 
quantities of which were mixed with the ore. Fuel and labor 
were very high, and the ore mixture already too siliceous. A 
rough method of sorting was instituted, and some twelve per cent, 
of the entire weight of the first-class ore was thrown out with 
the loss of scarcely any metal. The month’s average assay of ore 
due solely to this sorting was increased per cent., and the fur¬ 
naces gave an extra yield of 1,500 pounds of copper from 30 tons 
daily, or 45,000 pounds for the month, which, calculated on the 
spot at 10 cents per pound, was a gain of $4,500. The net gain 
was probably even more than this ; for the expense of sorting was 
hardly appreciable, while the increased fusibility of the charges, 
and the fact that 3,000 pounds of barren material could be replaced 
by an equal amount of good ore, added largely to the profits. 

All windows in the spalling-shed must be protected by strong 
iron wire netting, three meshes to the inch ; nor should the eyes 
of the workmen receive less care than the panes of glass. Acci¬ 
dents from flying fragments of sharp rock are common, and fre¬ 
quently result in a partial or total loss of vision, which entails 
serious expense on the company, and is an infliction almost 
worse than death upon the victim. All this can be easily avoided 
by the use of wire goggles, strongly and properly made, so that 
while completely protecting the visual organs, they cause but lit¬ 
tle annoyance to the wearer. These should be furnished by the 
employer, and should be constantly worn, on pain of dismissal. 
The workman, with proverbial recklessness, will sometimes claim 
that he has a right to risk his own eyes if he chooses; but the 


THE ROASTING OF COPPER ORES IN LUMP FORM. 




employer may demand the privilege of protecting himself against 
those claims which, with more or less reason, are sure to be made 
in case of injuries received while in his employ. Artificial warm¬ 
ing of the building is neither necessary nor desirable. Lithe, active 
men or boys, of nervous temperament and quick, accurate move¬ 
ments, should be selected for this work, which calls rather for 
rapidity and knack than for any great muscular effort. The 
amount of rock broken being about proportionate to the number 
of effective blows delivered, it follows that, other things being 
equal, a man who delivers twenty blows per minute will accom¬ 
plish nearly double the work of one whose deliberate tempera¬ 
ment would naturally limit his motions to half that number dur¬ 
ing the same time. It is just in this matter of selecting workmen 
adapted to each variety of labor that long experience in the man¬ 
agement of men, and a thorough knowledge of human nature, 
enable one man to obtain residts and effect improvements that 
seem well-nigh impossible to him who is unaccustomed to such 
a perfect adaptation of means to ends. 

The cost of spalling an ore or the same character as that on 
which the foregoing estimates for machine-breaking are based 
has been calculated from the average residts of a very large quan¬ 
tity of ore, assuming 100 tons to be spalled, screened, and loaded 
in ten hours. 

COST OP SPALLING ORE BY HAND WITH AN OUTPUT OF 100 TONS PER 

TEN HOURS. 

Labor: Per 100 tons. Per ton. 

14 men breaking ore, including screen¬ 
ing and loading, at $1.50.$21.00 

4 men sledging and loading at $1.50. . 6.00 

1 foreman. 2.50 $29.50 $0,295 

Repairs : 

Including new steel and handles. 

5 handles at 30 c.-. 1.50 

7 pounds of steel at 15 c. 1.05 

Blacksmith’s and other work on above, 

■J- day. 1.00 

Screens, forks, and shovels. 1.67 

General repairs. 0.55 

Sinking Fund: 

To replace screens and permanent 
fixtures. 


5.77 0.0577 


0.15 0.0015 


Total, 


$ 35.42 $ 0.3542 













56 MODERN AMERICAN METHODS OF COPPER SMELTING. 

This is about 25 cents per ton greater than by machine-break¬ 
ing. The same addition—50 per cent.—will here also cover the 
increased cost of breaking the ore smaller for kiln-roasting. 

I. HEAP-ROASTING. 

The roasting of sulphureted ores or copper in mounds or 
heaps dates back beyond the age of history, and in its most 
primitive form is still practiced among barbarous nations who 
have evidently never held communication with each other. It is 
not difficult to imagine its origin in the midst of some rude peo¬ 
ple, whose possession of superficial deposits of oxides and carbon¬ 
ates of copper had taught them the value of that metal as ob¬ 
tained by a simple process of fusion, while the sulphide ores that 
were doubtless encountered at a slightly greater depth were 
thrown aside in heaps as worthless until the spontaneous com¬ 
bustion of some of these waste-piles, brought about by the de¬ 
composition of the sulphides, and the interesting discovery that 
ores, hitherto considered valueless, would, after a simple burning, 
also yield the coveted metal, led some metallurgist of that day to 
the idea of calling in the aid of artificial combustion to hasten 
matters. Nor has this rude and simple process undergone that 
general improvement that one might have expected when consid¬ 
ering the tremendous advances made in other appliances for ac¬ 
complishing the same purpose. A somewhat careful inspection 
of nearly all the localities in the United States where heap-roast¬ 
ing is practiced reveals the fact that the results obtained are far 
from satisfactory in the greater number of instances. The 
amount of fuel employed and the height and size of the heap are 
not correctly proportioned to the sulphur contents of the particu¬ 
lar ore under treatment. Fragments of rock far exceeding in 
size the extreme proper limit, as determined by experience, are 
mixed with material so fine as to be fitted only for the covering- 
layer, and these are dumped upon the ill-arranged bed of fuel 
without regard to the final shape of the structure or the establish¬ 
ment and maintenance of the requisite draught. Also, a suffi¬ 
cient quantity of proper material for the all-important covering 
layer is not applied. The result of these and some other defi¬ 
ciencies is that a small proportion only of the ore is exposed to a 
proper degree of heat, and the remainder of the heap is pretty 
equally made up of half-molten masses of clinkers from the inte- 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


57 


nor, and comparatively raw and nnbnrned material from the outer 
layer. With the exception of what little sulphur may have been 
driven off by volatilization, the ore after such a calcination is 
scarcely better fitted for the fusion that is to follow than if it had 
not been roasted. The evil results of an imperfect preliminary 
calcination can only be fully appreciated after the ore has passed 
to the next stage of treatment; in fact, they are so far-reaching, 
that it is impossible to express the full measure of the damage in 
exact figures. A discussion of the effect of imperfect calcination 
and of its remedies will be found under the head of “ Smelting 
Sulphide Ores in Blast-Furnaces.” The vital importance of the 
process, and the almost universal want of care and supervision 
in the carrying out of its details, will justify this urgent remon¬ 
strance against its improper execution. Moreover, the cost of 
roasting properly is no greater than that of doing it imperfectly. 

The responsibility of selecting heap-roasting in contradistinc¬ 
tion to the other methods enumerated for the desulphurization of 
an ore must rest upon the metallurgist in charge of the works, 
and is a question deserving the most careful consideration; nor 
are the reasons for or against its adoption in most cases so clear 
and self-evident that plain and unvarying rules can be laid down 
for his guidance. In this, as in many other instances, there are 
usually strong metallurgical, commercial, and sanitary arguments 
that should be carefully weighed. The contiguity of cultivated 
land, or even of valuable forests, would forbid the employment 
of heap-roasting unless the arguments for its adoption were 
sufficiently powerful to outweigh the annoyance of constant re¬ 
monstrances on the part of the land-owners, accompanied by 
claims for heavy damages from the effect of the sulphurous gases. 
For legal reasons, as well as for various other prudential and 
sanitary motives, it is important to learn how this damage is 
effected, and to what distance its ravages may extend. 

1. The damage is caused solely by sulphurous and sulphuric 
acids, neither arsenical nor antimonial fumes nor the thick clouds 
of smoke evolved from bituminous coal having any appreciable 
influence. 

2. The most injurious effects are visible on young, growing 
plants; and the more tender and succulent their nature, the more 
rapid and fatal are these. 

3. A moist condition of the atmosphere greatly heightens the 


58 MODERN AMERICAN METHODS OF COPPER SMELTING. 

injurious effects of the gases, and as our most frequent rains oc¬ 
cur in the spring*, at the very period during which the crops and 
forests are in young, green leaf, more damage may be effected in 
a few days at this season than during the entire remainder of the 
year. The author has seen a passing cloud, while floating over a 
dozen active roast piles, absorb the sulphurous smoke as rapidly 
as it arose, and, after being wafted to a distance of some eight 
miles by a gentle breeze, fall in the shape of an acrid and blight¬ 
ing rain upon a field of young Indian corn, withering and curl¬ 
ing up every green leaf in the whole tract of many acres in less 
than an hour. 

4. As might be expected, the vegetation nearest the spot where 
the fumes are generated suffers the most, and the direction of the 
prevailing winds, in a fertile district, can be plainly determined 
by the sterile appearance of the tract over which they blow. 

The most elaborate means for obviating this evil have been 
tried at the great metallurgical establishments of Europe, and 
vast sums have been expended in this direction. The plans pur¬ 
sued in England tend more toward the mechanical deposition of 
the offending substances in long flues and passages (the first ex¬ 
perimenters evidently having failed to realize that the sulphur¬ 
ous vapors alone caused the damage), while in Germany, the more 
scientifically correct method of effecting condensation and absorp¬ 
tion of the gases by means of various liquids and chemicals was 
pursued, but with scarcely better results. In the former case, it 
was soon discovered that, while the oxides of zinc, lead, arsenic, 
antimony, and various other substances carried over mechanic¬ 
ally or as gases by the draught, were condensed and deposited 
so completely in the canals that the air issuing from the top of 
the tall chimney was practically free from them, the percentage 
of sulphurous and sulphuric acids, which alone are responsible 
for damage to vegetation, was not sensibly diminished. Similar 
efforts in Germany foi* the absorption of the sulphur gases were 
carried out with such imperfect and ill-adapted apparatus, and 
on so inadequate a scale, that the absolute impossibility of a suc¬ 
cessful issue must be apparent to any one reading the pamphlet 
issued by the Freiberg officials intrusted by government with the 
execution of the experiments. But however insufficient the ap¬ 
paratus, the results arrived at decisively indicated the impossibil¬ 
ity of disposing of the offending fumes by any plan of condensa- 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


59 


tion or chemical absorption, except on a small scale and with un¬ 
usually dilute gases. 

The problem has long been solved in Europe in the only ra¬ 
tional and economical manner, by utilizing the hitherto destructive 
fumes for the manufacture of sulphuric acid. This requires, of 
course, the abolition of heap-roasting, and the confinement of all 
processes of calcination to such closed kilns and furnaces as 
may be placed in direct communication with the leaden acid 
chambers. The very secondary position held by agriculture in 

those sections of our countrv that furnish the material for the 

*/ 

principal smelting-works has, up to the present time, obviated 
any necessity of dealing with this question, though some of the 
largest copper smelting-works in the East have already adopted 
the European solution of the problem as a matter of profit rather 
than necessity. 

In the case of smelting establishments of such capacity that 
not more than twenty-five tons daily of sulphur are oxidized and 
poured into the atmosphere, it is probable that all vegetation out¬ 
side of a circle of four miles in diameter may, under ordinary 
circumstances, be considered safe from the effects of the fumes. 

No harm to man or beast has ever been authentically reported 
as resulting from the use as food of an article of vegetable origin 
that has been exposed to the corrosive influence of such gases. 
This is a very important point, and careful investigation and ex¬ 
periments have completely disproved the opposing arguments so 
often made against smelting-works in Germany by certain stock- 
raisers. 

During the preparation of the new edition of this book, Butte 
City, Montana, is anxiously seeking a remedy for the vast clouds 
of sulphurous vapors that daily arise from the treatment of its 
rich, sulphureted copper ores. By a rough estimate, there are 
probably not less than 200 tons daily of sulphur thus oxidized 
and escaping into the atmosphere, forming a nuisance that must 
be experienced to be appreciated. 

As I have already intimated, several carefully-formed Euro- 
pean commissions have investigated the question of handling 
these fumes with more care and skill than is likely to be brought 
to bear upon the matter by any private enterprise, however liber¬ 
ally endowed. 

«/ 

The result of their investigations indicated that the only 


GO MODERN AMERICAN METHODS OF COPPER SMELTING. 

rational method of combating this nuisance was to utilize the 
noxious gases that had hitherto been allowed to escape into the 
atmosphere, and for this purpose, immense lead chambers were 
built, and nearly all the calcining apparatus arranged to discharge 
their fumes into the latter, in which they were converted into 
sulphuric acid by the usual means; the result being not only a 
total cessation of the nuisance, but a quite satisfactory profit 
therefrom. 

At Butte City, owing to its isolation and consequent high 
freight rates to a market, the direct manufacture of sulphuric 
acid could not be undertaken with any hope of profit. 

From a personal knowledge of the conditions that prevail in 
Montana, and after careful consideration of the same, I can see 
only one feasible and economical plan for the abatement of the 
fumes. I should suggest: 

1. An entire abolition of heap-roasting, substituting therefor 
stall-roasting, or kiln-roasting, according to the character of the 
ore. 

2. Such an arrangement of furnaces and flues that the sul¬ 
phur fumes may be obtained in as concentrated a form as possible, 
to be used as described in paragraph No. 3. 

3. The utilization of these sulphurous acid gases for precipi¬ 
tating the copper as a dichloride, and eventually producing it in 
a metallic form from a solution obtained by calcining and dis¬ 
solving the copper-silver mattes, which form the main product of 
all the smelting-plants, and are now mostly shipped to Europe 
for separation and refining. By the new Hunt & Douglas, 
method, the fumes are thus converted into sulphuric acid with¬ 
out the necessity of any costly lead chambers, or the ordinary 
cumbersome and expensive paraphernalia of an acid-plant, and 
thus used directly in treating the mattes, and obtaining a copper 
of the highest quality, which by one simple refining operation is 
put into ingot equal to Lake copper for most purposes. The 
silver and gold are obtained from the residues by the ordinary 
methods. 

4. The sulphur fumes arising from those operations which 
fail to produce a gas sufficiently concentrated for the purpose 
just indicated, should be discharged into the upper regions of 
the atmosphere by means of very high chimneys, as is done at 
all chemical works in the neighborhood of cities, and with per- 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


61 


feet success ; the fumes being so diluted with air before they reach 
the ground as to be absolutely harmless to vegetable life, as well 
as imperceptible to the human senses. 

It has been satisfactorily demonstrated, by the evidence of 
long, practical trial, as well as by elaborate experiments, that so 
small a proportion of arsenic as exists in ordinary sulphureted 
fumes is perfectly harmless both to man and beast. 

Within a few months, a New York firm has brought out a 
condenser, which claims to completely abate the fume nuisance. 
If it were not endorsed by first-class metallurgists, I could scarcely 
believe that so small an apparatus could produce so great a re¬ 
sult. It is worthy of investigation. / 

In laying out the ground for roast-piles, the first point to con¬ 
sider is the prevailing direction of the wind, great care being 
taken that the fumes shall neither be blown toward the works 
themselves, nor toward the offices and dwelling-houses in their 
immediate neighborhood. Smelting-works are frequently situ¬ 
ated in a valley, in which the prevailing winds naturally follow its 
longitudinal axis. In this case, a tract of ground on one side or 
other of the central depression, instead of in its immediate course, 
should be selected. By careful observation, and taking into con¬ 
sideration that the prevailing winds may differ at different sea¬ 
sons of the year, the roast heaps can generally be so placed as to 
give no substantial ground for claims of damage to agriculture. 
Care should also be taken that the selected tract is free from any 
possible chance of inundation ; that it is either perfectly dry, or 
susceptible of thorough drainage; that it is not crossed by gullies 
or depressions that may serve as water-courses for the drainage 
of the surrounding hills in case of a heavy shower; that it is pro¬ 
tected as far as possible from violent winds; that snow does not 
drift on it badly in winter, and that it is at least as high as the 
spot to which the ore is to be transported for the ensuing opera¬ 
tion, or, if this is not feasible, at least as high as the elevator 
which is to raise it to the required level. If possible, it should 
occupy an intermediate position, as regards grade, between the shed 
in which the ore is prepared for roasting and the point at which 
the calcined product is to be delivered. A fall of ten feet for the 
first step and four and one-half or more for the second—total four¬ 
teen and one-half feet—will render possible the establishment of a 
system of handling and transportation that can hardly be excelled. 


62 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


A detailed description of such a model plant will suffice as a 
pattern that may be varied to suit local conditions, always re¬ 
membering that, under ordinary American circumstances, the 
economy of labor is one of the first conditions to be observed, 
and that the saving ot 25 cents in handling a ton of crude ore is 
equal to a dollar or more on the ton of matte, and at least two 
dollars when estimated on the ton of copper. 

Assuming that the metallurgist is called upon to prepare a 
yard for lieap-roasting of ample size to contain a sufficient num¬ 
ber of piles to furnish from 80 to 100 tons daily of calcined ma¬ 
terial, without encroaching upon the partially burned ore, and 
that the contour of the ground permits the requisite fall in each 
direction—as already explained—the following plan may be ad¬ 
vantageously adopted: 

Experience having demonstrated that an ordinary pile 40 feet 
long, 24 feet wide, and 6 feet high will contain about 240 tons, 
and burn for 70 days, to which should be added 10 days for re¬ 
moving and rebuilding, it follows that each pile will supply - 2 8 4 F ° 
= 3 tons of roasted ore daily; so that 35 heaps will be needed to 
furnish the full amount of 100 tons daily. Allowing 36 feet for 
the width of each structure, and 60 feet for the length, in order 
to give ample room for various purposes that will be explained 
hereafter, an area of 75,600 square feet will be required. 

The frost being out of the ground and the surface dry, a rec¬ 
tangular area of the extent just computed should be prepared by 
means of plow and scraper, being leveled to a perfect plane, and 
having a slight slope toward one longitudinal edge, or from a 
central ridge toward either side. The black surface soil should 
be removed, together with all sods, stumps, and remains of vege¬ 
tation, and the space that it occupied replaced with broken stones, 
slag, or coarse tailings from the concentrator; or, best and cheap¬ 
est of all, granulated slag from the blast-furnace. This can be 
easily obtained in any desired amount by allowing the molten 
scoriae from the slag-spout to drop into a wooden trough, lined 
with sheet iron, placed with a grade of one inch to the foot, and 
provided with a stream of water running through it, equal to at 
least, sixty gallons a minute. If sufficient fall is available, the 
granulated slag—graduated to any desired size by the height 
through which it falls, velocity and amount of water, and various 
other trifling factors easily ascertained by trial—is discharged 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


63 


directly from the launder into dump-carts, the water being* drawn 
off by substituting* a sieve of ten meshes to the linear inch for the 
lower eighteen inches of the wooden trough bottom. By this 
simple means, the best kind of filling can be prepared and deliv¬ 
ered at the roasting-yard for nothing, the expense of transporta¬ 
tion hardly equaling the wages of the ordinary slag-men, who may 
be employed in attending* to the loading of the carts and the 
leveling of the material when dumped. The entire area of the 
rectangle being raised at least two inches above the surrounding 
ground, a proper surface is formed by spreading upon the foun¬ 
dation already described a sufficient quantity of clayey loam. 
This should be rolled several times with a heav^ roller drawn by 
horses, the surface being* slightly dampened from time to time, 
until the entire area is as level and nearly as hard as a macad¬ 


amized road. 

Unless the climate is an unusually dry one, and the district 
free from snow, it will be better to use gravel instead of the loam, 
putting down a layer some four inches thick over the entire sur¬ 
face of the roast-vard. This will prevent mud, and the great loss 
arising from the treading* of the fine ore into the same. 

If the roast-yard is to be a permanency, and one is desirous of 
obtaining the best results with the least loss, a final covering* of 
ore-fines should be added, the gravel being* covered three or four 
inches deep with low-grade fines. Nor should this covering* be 
confined merely to the portion of the ground that is to be occu¬ 
pied by the ore-heaps, but should be applied to the entire surface, 
including spaces between the heaps, passageways at ends of heaps, 
etc., etc. By so doing, there will always be a caked coating of 
ore-fines to shovel on, and the danger of getting dirt and gravel 
mixed with the roasted ore will be avoided completely. 

As the layer of fines beneath the heaps becomes gradually 
roasted through, it should be removed with the coarse ore and 
sent to the furnaces, its place being supplied by fresh fines of the 
richest description, for nowhere can fine ore be roasted so free 
from any possibility of loss as when safely buried beneath the 
heap. 

Nothing is more important about a roast-yard than a proper 
drainage system. If possible, the entire ground should slope 
slightly toward the lateral lower track on which the roasted ore 
is removed to the furnaces; and where such a gentle slope can 


64 MODERN AMERICAN METHODS OF COPPER SMELTING. 

be obtained, the drainage problem is rendered very simple and 
perfect; for a deep ditch run all along the upper edge of the 
mound, parallel with the track just referred to, will cut off all the 
surface water from the ground beyond, and leave to deal with 
only the small amount of water that falls on the roast-yard itself. 
This water is best removed by tile drains, laid underground, with 
frequent openings at suitable places, where there is no danger of 
fine ore being washed into the drain. 

They will, of course, have their discharge through the bank- 
wall into the ditch that runs between the lower track and the 
bank-wall. Assuming a fall of some ten feet between the spall¬ 
ing-shed and the ground under consideration, an elevated track is 
constructed over the central longitudinal axis of this rectangle, 
for the purpose of delivering the broken ore upon the heaps. 
Where no side-hill is available, the ore is carried up on to the 
heaps in wheelbarrows. The trestles to support the track may 
consist of sets or bents of two 8-inch by 12-inch posts with 8-inch 
by 10-inch caps six feet long. Bents 36 feet apart and properly 
braced. The posts should be about six feet apart at the bottom 
and two or three feet apart at the top. 

These bents support the trussed beams, 10 inches by 12 
inches, on edge, which carry the track as shown in the accom¬ 
panying sketch. These girders may be made up of 2-inch or 
3-inch planks spiked together. 

A fall of an inch in 12 feet will greatly facilitate the handling 
of the loaded car, and offer little obstruction to the return of the 
empty one. The track should, if possible, consist of T- rails, 12 
pounds to the yard, firmly spiked to the longitudinal stringers, 
no sleepers being necessary; and well connected with each other 
by fish-plates, having two half-inch bolts at each end of each rail. 
All tracks throughout the entire establishment should have the 
same gauge; 22 inches is a convenient standard. 

An iron-bodied end-dumping car, so made as to dump at right 
angles to the track, should be used. As the heaps are some 40 
feet in length, the area over which the ore can be distributed by 
dumping from the car is far too contracted, and the following 
simple contrivance will be found to save many thousand dollars 
annually that would otherwise be expended in spreading the ore 
by hand: a plate of f-inch boiler iron, 30 inches square, fitted 
with a pair of short, low rails, on three sides of it, is so cut and 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


65 

















































































MODERN AMERICAN METHODS OF COPPER SMELTING. 


06 

placed upon the stationary track that the loaded car, striking 
lirst the flattened extremities of one set of the short rail pieces, 
while the flanges of the wheels run in corresponding slits until 
elevated upon the turn-table by the gradually increasing height of 
the short rails referred to, the heavy car may be easily turned 
upon the greased plate by a single workman, being held and 
guided to the similar pair of short rails placed at right angles to 
those already described by a circular guard rail, fastened at that 
end of the plate opposite to the point of entrance. A temporary 
track, formed of a pair of heavy rails, held firmly together, pre¬ 
vented from spreading by cross-ties, and supported by movable 
trestles, is laid at right angles to the main railroad, correspond¬ 
ing exactly to a pair of the short side rails on the turn-table plate. 
It will be readily seen that, by this simple contrivance, the ex¬ 
treme end of the longest roast-pile can be reached with the loaded 
car, while the turn-table plate can be shifted backward and for¬ 
ward until every square foot of the heap has received its proper 
quota of ore. The accompanying dimensioned drawing illus¬ 
trates sufficiently the principal arrangements described in the pre¬ 
ceding pages. If the contour of the surface permit, one longi¬ 
tudinal side of the prepared yard should be bounded by a wall 
about four feet in height, the top of the same being level with 
the ground on which the roast-heaps are built, while a railroad 
leading to the furnaces is constructed parallel with it, in such a 
manner that the calcined ore may be wheeled on a plank and 
dumped directly into cars without having to ascend any grade, 
thus greatly lessening the expense of loading. The labor and 
cost of preparing a plant, such as has been just described, will be 
quickly repaid by the consequent avoidance of the waste insepa¬ 
rable from a moist and muddy roasting yard, and especially from 
water flowing between the heaps. A case came under the author’s 
observation, where the want of proper facilities for carrying off 
surface water caused a loss estimated at $12,000 within an 
hour, merely from the material washed away by the back-water 
from a swollen ditch, which passed between the roast-heaps, but 
which, from motives of economy, had been made too small to 
carry off unusual floods. 

The height of the pile must depend entirely upon the charac¬ 
ter of the ore and the time for calcination at the disposal of the 
metallurgist. The higher the heap, the more fiercely it will heat, 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


67 


and the longer it will take to complete the operation. Conse¬ 
quently, where- the ore is rich in sulphur, and when time is an 
object, as where the supply for the furnaces is small, heaps should 
be made low. 

An ore with 12 per cent, sulphur, which is, perhaps, as low as 
can be thoroughly roasted in heaps without the intermixing of a 
considerable quantity of fuel throughout with the rock, may be 
piled up to a height of 7 feet advantageously, while solid pyrites 
with a sulphur tenor of from 35 to 40 per cent, should never be 
allowed to exceed 5 or 54 feet, the measurement including only 
the ore, and not the layer of wood on which it rests. The best 
average height for ordinary ore is 6 feet, under 7 which circum¬ 
stances it will burn 70 days; the time being correspondingly di¬ 
minished or increased by 10 days, if 6 inches be taken from, or 
added to, the above figures. The area of the heap has little in¬ 
fluence on this time. The following table gives the result of the 
roasting of large quantities of various ores. In most of these cases, 
frequent sulphur assays were made of the ore under treatment; 
but in a few instances, the sulphur was estimated from a general 
knowledge of the material. The heaps were thoroughly covered 
and carefully watched, and the combustion was kept at the lowest 
point compatible with safety, the sole object being to obtain the 
most thorough possible roast, regardless of time or trouble. 

This should lie the universal practice; for although the grade 
of metal to be produced in the subsequent fusion may not demand 
such a thorough calcination, it is better to roast a certain portion 
of the stock thoroughly, and then reduce, or dilute, the matte to 
the required standard by the addition of raw ore. This lessens 
expenses in various ways. It costs but little more to roast an ore 
thoroughly than to do so partially; and the more completely the 
sulphur is eliminated from the roasted ore, the larger will be the 
proportion of raw ore that can be used in the charge; and conse¬ 
quently, the less will be the cost of calcining and the losses from 
fines of roasted ore. It is also very easy to keep the “ pitch ” or 
percentage of the matte produced at a proper point, when 
thoroughly oxidized stock is always at hand. These, and vari¬ 
ous other reasons that could be mentioned, are sufficient to re¬ 
fute the arguments of those who consider the addition of raw ore 
peculiarly injurious, and prefer an imperfect roasting of the en¬ 
tire stock. 


68 MODERN AMERICAN METHODS OF COPPER SMELTING. 


LENGTH OP TIME CONSUMED IN 

BURNING 

HEAPS OF 

VARIOUS 

HEIGHTS. 

Height 
in feet. 

Quality of ore. 

Per cent. 

Per cent. 

Days 

No. of 

sulphur. 

copper. 

burning 

sample. 

5. . 

. Pyrite. 

39 

61 

54 

No. 1 

5. . 

. Clialcopyrite, with little py¬ 
rite in quartz. 

18 

14-3 

41 

“ 2 

5.. 

.Bornite and pyrite. 

31 

21-4 

53 

“ 3 

H- 

. Same as No. 1. 

39 

6* 

G6 

“ 4 

5|. 

. “ “ No. 2. 

18 

14-3 

50 

“ 5 

5£. 

. “ “ No. 3. 

31 

21-4 

65 

“ 6 

6.. 

. “ “ No. 1. 

39 

6£ 

72 

“ 7 

6.. 

. “ “ No. 2. 

18* 

14-3 

61 

“ 8 

6. . 

. “ “ No. 3. 

31 

21-4 

74 

“ 9 

7.. 

. “ u No. 1, much matted 

39* 

6i 

94 

“ 10 

7 .. 

. “ “ No. 3. 

31 

21-4 

86 

“ 11 

7£. 

.Copper glance and pyrite in 
quartz. 

20* 

23-4 

54 

“ 12 


* Estimated. 


The area of the heap is determined by the position and size 
of the ground at disposal, and the convenience of delivering the 
ore. Its width is limited by the distance to which the covering 
material can be conveniently thrown with a shovel, and by the 
room between the bents that support the track. 24 feet in width 
by 40 in length is a very convenient size, smaller heaps demand¬ 
ing considerably more labor and fuel to the ton of ore. With 36 
feet between the bents, an ample border of 6 feet will be left on 
each side of the pile for collecting the fines, wheeling the same 
wherever required, and fully securing the wood-work against all 
danger of fire. Risk from fire is further obviated by elevating 
the foundation sill from which the uprights arise, upon a wall of 
slag-brick, 3 feet or more in height. A pile of the dimensions re¬ 
ferred to, 24 feet by 40 feet square, and 6 feet high, will contain 
about 240 tons of ordinary ore, and should be built in the follow¬ 
ing manner 

The corners of the rectangular space on which it is to be 
erected should be indicated by stakes, or, if the same size is to be 
permanently retained, by large stones, or better, blocks of slag, 
imbedded in the ground. The sides of the area being indicated 
by lines drawn on the ground to guide the workman, the entire 


* Subsequent experience lias shown that it is more economical to still 
further increase the size of the heaps, 40 by 80 ft., and 7 ft. high is none too 
large. 

















THE ROASTING OF COPPER ORES IN LUMP FORM. 


69 


space should he covered evenly to the depth of four or six inches 
with fine ore from the spalling-shed. This layer of sulphides 
answers several purposes: in the first place, it prevents the bak¬ 
ing and adhering to the ground of the coarser ore, which, espe¬ 
cially when much matte is formed, sticks to the clayey soil to such 
an extent as to tear up and injure the foundation, besides mix¬ 
ing worthless dirt with the ore, and causing a loss of the latter 
when attempts at separation are made. It also forms a distinct 
boundary line between the worthless and valuable materials, and, 
when left undisturbed during two or three operations, becomes 
itself so thoroughly desulphurized that the upper half or more 
may be scraped up with shovels and added to the roasted ore, its 
place being filled by a fresh supply of fines. This operation com¬ 
pleted, the fuel is next arranged by an experienced workman in 
a regular and systematic manner. The quality and size of the 
wood is a matter of some moment, and must be determined for 
each individual case, it being evident that that variety of fuel 
that yields the greatest amount of heat for the longest time pos¬ 
sesses the highest money value, provided the ore is of such a na¬ 
ture as to bear the temperature produced without fusing. As 
most sulphide ores will not stand the heat generated by a thick 
bed of sound, dry, hard wood, it frequently happens that a 
cheaper variety answers the purpose better. The outside border 
of wood that corresponds to the edges of the heap should be of 
better quality, as no such degree of heat is attainable there as in 
the interior of the pile. Therefore a large proportion of the bed 
may be made up of old rails, logs, gnarled and knotted trunks 
that have defied wedge and beetle, and such sticks of cord-wood 
as are daily thrown out from wood-burning boilers and calcining- 
furnaces as too crooked and misshapen to enter a contracted fire¬ 
place. Such miscellaneous fuel causes somewhat greater labor in 
arrangement; but whatever the material, it must be placed with 
such care and skill as to form a solid and sufficient bed, varying 
in depth from 8 to 14 inches, according to the behavior of the 
ore. However rough and irregular the greater portion of the 
fuel at our disposal may be, enough cord-wood of even length 
and diameter should be selected to form a four-foot border 
around the entire heap and just within the side-lines of the area; 
for the even and regular kindling of the heap depends consider¬ 
ably upon the proper arrangement of this border. Sticks of cord- 


70 MODERN AMERICAN METHODS OF COPPER SMELTING. 


wood not. larger than 5 inches in diameter should be laid side by 
side across both ends and sides of the area. Across this layer, 
small wood is again piled until this four-foot border has been 
built up to the height of some 10 inches, brushwood and chips 
being scattered over the surface to fill up all interstices, while 
canals 6 inches wide, filled with kindlings, are formed at intervals 
of 8 or 10 feet, leading from the outer air and communicating 
with the chimneys in the center line of the heap. The empty 
area within this encircling border is now filled with the poorer 
quality of fuel, all sticks laid parallel and with as much regularity 
as possible, to cover all cracks and interstices, that no ore may 
fall through the wood, and to cover over the draught-canals in 
such a manner that they shall be neither choked nor destroyed 
by the superincumbent load.* 

The chimneys, which assist materially in rapidly and certainly 
kindling the entire heap, are formed of four worthless boards 
nailed lightly together in such a manner that two of the opposite 
sides stand some eight inches from the ground, thus leaving 
spaces that communicate with the draught-canals referred to, and 
toward which several of the latter converge. For a heap 40 feet 
in length, three such chimneys, eight inches square, will suffice. 
They should project at least two feet above the proposed upper 
surface of the structure, that no fragments of ore may accident¬ 
ally enter the flue opening and destroy its draught. In certain 
localities, where even old boards are too valuable to be needlessly 


sacrificed, two or three medium-sized sticks of cord-wood may be 
wired together to form the chimney; or old pieces of sheet-iron, 
such as condemned jig-screens, worn-out corrugated roofing-iron, 
etc., may be so bent and wired as to form a permanent and suffi¬ 
cient passage, while this material will answer for several opera¬ 
tions. The chimneys being placed in position, equidistant, and 
on the longitudinal center line of the bed of fuel, and held up¬ 
right by temporary wooden supports, the heap is ready to receive 
the ore. This is brought in car-loads of 1,500 or 2,000 pounds 
from the spalling-shed, and weighed en route on track-scales. It 
is dumped on a portable wooden platform about eight feet square, 


*An excellent paper on heap roasting in Vermont, by Mr. William 
Glenn, may be found in the Engineering and Mining Journal for December 
8, 1883. 





THE ROASTING OF COPPER ORES IN LUMP FORM. 


71 


to prevent t-lie deranging’ of the wood from the fall of so heavy 
a mass of rock from a height of ten feet or thereabout. The 
first few car-loads are heaped about the chimneys, and the plat¬ 
form is changed from place to place as convenience demands, 
until the bed of wood is thoroughly protected by a thick layer of 
ore. The remainder of the process is a very simple operation. 
The cars of ore are dumped in turn over the entire area by a sys¬ 
tematic shifting of the temporary pair of rails already described, 
and the heap formed into a shapely pyramid, with sharp corners 
and an angle of inclination of some 42 degrees, or as steep as the 
ore will naturally he without rolhng. The main body of the 
structure is formed of the coarsest class of ore; the ragging is 
next placed upon the pile, forming a comparatively thick cover¬ 
ing at the part nearest the ground, and gradually thinning out 
toward the top and on the upper surface. Its thickness depends 
on the amount available, and no fears need be entertained of its 
having an unfavorable influence on the calcination; for when 
carefully separated from the finest class, a heap formed entirely 
of ragging will give reasonably good results. The extreme out¬ 
side edge of the ore, when all is in place, should not entirely cover 
the external border of wood. At least a foot of uncovered fuel 
should project beyond the layer of ragging, both to prevent the 
ore from sliding off its bed as well as to insure a thorough 
kindling of the outer covering of mineral. The amount of wood 
required properly to burn a heap of 240 tons of ore will vary 
greatly with the composition of the latter, standing in direct pro¬ 
portion to its sulphur contents, and especially to the amount of 
bisulphides present, but may, on the average, be estimated at 12 
cords, or one cord of wood to 20 tons of ore. In smaller heaps, 
this proportion must be considerably increased. 

The fine ore that is to form the external layer, and on which 
depends largely the success of the process, is seldom placed upon 
the heap until after it is fired. Perhaps the most judicious prac¬ 
tice is to cover the sides of the pile with a very thin layer, scatter¬ 
ing it evenly with a shovel, and leaving the upper surface, as well 
as a space eighteen inches broad at the bottom, uncovered; for if 
the fine ore is thrown carelessly upon the lower circumference of 
the pile, the draught is decidedly hampered and the fire stifled 
before getting fairly under way. For an average ore, an amount 
of fines equal to 10 per cent, of its total weight is ample j of this, 


72 MODERN AMERICAN METHODS OF COPPER SMELTING. 

eight tons may he strewn lightly upon the sides of the heap, as 
just described, the remaining 16 tons—assuming the entire con¬ 
tents to be 240 tons—being arranged in small piles upon the 
empty space between the roast-heaps, where it is easily accessible 
to the shovel. The lighting should be done just as the day shift 
is quitting work, as the dense fumes of wood smoke, strongly 
saturated with pyroligneous acid and the various gaseous com¬ 
pounds of sulphur and arsenic, among which sulphureted hydro¬ 
gen is always plainly distinguishable, are almost unbearable. 

If possible, fine weather should be selected for this purpose; 
for although no ordinary rain is capable of extinguishing a 
well-lighted roast-heap, it may still interfere greatly with kin¬ 
dling a new one, and is quite likely to cause subsequent irregulari¬ 
ties in the course of the process. There are several different 
methods of filing a roast-heap—such as lighting it only on the 
leewmrd side, and letting the fire creep back against the wind, 
kindling it through the draught-chimneys, etc., each of which 
has its advocates among roasting foremen; but long-continued 
observation has shown that no advantage is gained by any of 
these irregular methods, and the most sensible and successful 
practice is to fight it as quickly and thoroughly as possible by ap¬ 
plying a handful of cotton waste, saturated with coal oil, or a 
ladle of molten slag, to the kindling-wood at the mouth of each 
of the draught-canals, these being some six or eight in number, 
as already described. As the success of the entire operation de¬ 
pends principally on the management of the heap for the first 
few days after kindling, it will be necessary to study somewhat 
in detail the phenomena that it should normally exhibit during 
this critical period, always bearing in mind the impossibility of 
laying down any fixed rules that shall apply to all circumstances 
and to every variety of material 

Under ordinary circumstances, the heap may best be left en¬ 
tirely to itself for from four to six hours after fighting, care 
merely being taken that the kindling burns freely, and that the 
draught-holes communicate with their respective chimneys. At 
the expiration of this time, if the fire has spread v r ell over the 
entire area, about one-half of the remaining fines that have been 
provided for covering should be scattered lightly upon the heap; 
the low r er border and upper surface, which have hitherto been left 
unprotected, now receive a thin application, w hil e the lateral 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


73 


•'coating’ is rendered somewhat thicker and more impervious. If 
matters pursue a normal course, the early morning—twelve hours 
after firing—should see the heap smoking strongly and equally 
from innumerable interstices produced by the settling of the 
whole mass, due to the disappearance of the thick foundation of 
fuel. Dense pillars of opaque, yellow smoke, smelling strongly 
of sulphurous acid, arise from the site of each chimney; although 
if these were constructed of wood, no sign of them will remain 
except a few charred fragments, resting in a slight depression, 
which marks their sites. The entire surface will be found damp 
and sticky, and the covering material will have already formed 
quite a perceptible crust, from the adhesion of its particles. This 
“ sweating,” as it is termed, arises from the distillation products 
of the fuel—owing to its very imperfect combustion—and from 
the moisture contained in the ore. A yellowish crust surround¬ 
ing the vents from which the strongest currents of gas are seen 
to issue indicates the presence of metallic sulphur, the volatiliza¬ 
tion of the first loosely bound atom of which begins soon after 
the wood is fairly lighted. Its quantity depends on the propor¬ 
tion of bisulphides in the roast, as well as on the freedom with 
which air is admitted; the scarcity of oxygen and a rather low 
degree of heat favoring its direct volatilization, while an abun¬ 
dance of air and a comparatively elevated temperature influence 
the plentiful generation of sulphurous acid. 

During this first day, the newly kindled heap Anil require 
close and constant attention to prevent any undue local heating; 
nor is it at all uncommon to find that some neglected fissure has 
increased the draught to such an extent as to cause the sintering 
or partial fusion of several tons of ore at that point. The princi¬ 
pal signs by which the experienced eye judges of the condition 
of affairs are the color of the gas and the rapidity with which it 
ascends; the amount of settling and consequent Assuring of the 
covering layer; and, above all, the degree of heat at different 
parts of the surface. A light, bluish gas, nearly transparent, and 
ascending in a rapid current, is a sign that the heat is too great 
at that point, and the admission of air too free. The Assuring of 
the crusted covering material, after the general and extensive 
sinking caused by the consumption of the fuel, indicates a rapid 
settling that can only arise from the melting together, and conse¬ 
quent contraction, of the lumps of ore. All these conditions are 


74 MODERN AMERICAN METHODS OF COPPER SMELTING. 

met by a single remedy j that is, covering the surface at that 
point more thoroughly with fines, by which means the air is ex¬ 
cluded, the rapidity of the oxidation process diminished, and the 
temperature lowered. It should not be supposed that, because 
the interstices that exist in the upper part of the heap alone show 
evidences of heat and gas, those cracks and openings that have 
been left nearer the ground are of no importance; these are the 
draught-holes, while the former constitute the chimneys, and it 
is to the condition of the lower border of the pile that our at¬ 
tention should be most frequently directed in regulating the 
proper admission of air. A few shovelfuls of fine ore judiciously 
applied at the base of the heap will often have more effect than 
a car-load scattered aimlessly over the surface. 

Only an experienced laborer can manage a roast-heap to the 
best advantage, nor is it possible to establish fixed rules for the 
guidance of this process, varying conditions demanding totally 
different treatment. In a general way, it may be said that, after 
somewhat subduing the intense heat caused by the sudden com¬ 
bustion of so large an amount of wood, the attendant should con¬ 
fine himself to scattering the covering material in a thin layer 
over the sides and top of the structure, and effectually stopping 
up such holes and crevices as seem to be the vents for some un¬ 
usually heated spot below. 

By the third day large quantities of sublimated sulphur will 
be found upon the surface, in many places melting and burning 
with a blue flame. It is now necessary for the attendant to as¬ 
cend to the top of the heap, to properly examine the upper sur¬ 
face, and place additional covering material on such portions as 
still seem too hot. In doing this, a disagreeable obstacle is en¬ 
countered in the clouds of sulphurous gas, which, to one unac¬ 
customed to the task, seem absolutely stifling. By taking ad¬ 
vantage of then* momentary dispersion by currents of air, and 
retreating when they become too thick, no difficulty need be ex¬ 
perienced in covering the upper surface of the heap as thoroughly 
and carefully as any other part of it. 

If the process of combustion seems to have spread equally to 
all parts of the pile, nothing need now be done except daily to scat¬ 
ter a few shovelfuls of fines over such heated spots as seem to re¬ 
quire it; but if any isolated corner of the heap has failed to kindle, 
or, having once caught fire, has now become cold and ceased to 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


75 

smoke, it is necessary to draw the fire in that direction. This can 
he accomplished with ease and certainty by any one accustomed to 
the work; for there is no danger of a roast-heap becoming extin¬ 
guished when once fairly kindled. Certain isolated spots—es¬ 
pecially corners and angles—may fail to become properly ignited, 
but by opening a few draught-holes in the neighborhood the fire 
will surely spread wherever unburned sulphides still exist. Be¬ 
ginning at the end of the first week, and continuing for a month 
or more, a certain amount of sulphur may be obtained by form¬ 
ing 18 or 20 circular, ladle-shaped holes about 14 inches in di¬ 
ameter and 7 inches deep in the upper surface of the heap, and 
lining them carefully with partially roasted fine ore, so that they 
may retain the molten metalloid. The impure sulphur may be 
ladled out twice a day into wooden molds $ but the impurity of 
the product, caused by the great quantity of ore-dust and cinders 
constantly falling into the melted material, and the extremely 
scant production of a substance that is hardly worth saving, dis¬ 
courages the general adoption of the practice, although at some 
of the older German works it is still kept up. Experiments made 
with the greatest possible care saved only one-tenth of one per 
cent, of the total weight of the ore from a 30 per cent bisulphide 
ore. 

With certain varieties of ore, the sulphur, instead of collect¬ 
ing in a concentrated form at the principal issuing vents of the 
strongest currents of gases, condenses over the entire surface in 
a thin layer, and upon melting cements and agglutinates the fine 
particles of the covering layer in such a manner as to form an 
almost impermeable envelope. In such cases this crust must be 
destroyed, from time to time, with an iron garden-rake, or the 
process of calcination may be delayed for weeks beyond its cus¬ 
tomary limit from the lack of sufficient oxygen to maintain the 
proper rate of combustion. If arsenic is present, even in the 
smallest quantities, it will soon make itself visible as beautiful 
orange-colored realgar, AsS, and minute clusters of white, glisten¬ 
ing crystals of arsenious oxide, which usually form at the upper 
orifices of the accidental draught-canals that communicate with 
the interior of the heap. 

A strong and persistent wind from any one direction has an 
unfavorable effect on the process of heap-roasting, driving the 
fire toward the leeward side, and cooling those portions that feel 


7(5 MODERN AMERICAN METHODS OF COPPER SMELTING. 


the direct influence of the air-current to such an extent that one- 
fourth or more of the heap may remain in a raw condition. It 
is a somewhat remarkable fact that, while it is almost impossible 
to quench a roast-heap with water, unless completely flooded for 
a considerable length of time, a simple excess of the very element 
most favorable to its perfect combustion should have the power 
to extinguish it. If this annoying circumstance repeats itself 
with any frequency, it will be necessary to erect a high board 
fence on that side of the yard whence the most persistent winds 
prevail. Rain and snow have little influence on the course of the 
process, except in so far as they may cause serious chemical and 
mechanical losses. It is only after a heavy shower or sudden 
thaw that the great advantage of numerous and well-preserved 
ditches surrounding the entire area, and even leading between 
the heaps themselves, is fully realized and appreciated. When 
wet weather supervenes, after a long period of drought, the 
amount of copper dissolved from the soluble sulphate salts formed 
during the extended term of dryness may be so large as to repay 
some efforts to recover it. By simply leading the drainage from 
the roast-yard into two old brewer’s vats partially filled with 
scrap-iron, during one summer, 3,546 pounds of 40 per cent, pre¬ 
cipitate were collected. 

During the last two-tliirds of the life of the roast-heap it 
hardly requires an hour’s labor, and if the works possess an am¬ 
ple stock of roasted ore in advance, nothing further need be done 
to the pile until it has burned itself out and becomes sufficiently 
cool to handle. The daily inspection, however, should never be 
omitted ; for even at this advanced stage of the process, irregular 
settling or swelling of some portion of the structure may cause 
sufficient Assuring and consequent admission of air to produce 
serious matting, a disaster that the application of a single shovel¬ 
ful of fines at the beginning of the trouble would have prevented. 
In fact, it is far better to leave the heap undisturbed, unless good 
reasons exist for breaking into it, as the agglutinated covering 
material forms a roof almost impermeable to rain and wind, while 
the freshly calcined ore, when exposed to these elements, neces¬ 
sarily undergoes a serious waste. But if, as is in most instances 
the case, the demand for ore from the smelting department ex¬ 
ceeds the supply from the mine, but scant time can be afforded 
to the intermediate steps, and the calcination must suffer. If, 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


— *-r 

i ( 


therefore, it is the object to utilize, at the earliest possible mo¬ 
ment, the ore that is stored up in the heaps, they should be 
closely watched, and whatever portions of the same—usually the 
ends and corners—are found to be moderately cool, should be 
carefully stripped and broken into, the object being- to cool the 
ore that is already roasted, and extinguish the last remains of 
fire as rapidly as possible, without interfering too seriously with 
the process of oxidation that is continuing in the main body of 
the pile. This is accomplished by digging away the calcined ore, 
and following up the line of fire as it recedes from the surface 
toward the center, without approaching it so closely as to com¬ 
pletely extinguish it in that portion of the ore not yet properly 
calcined, which is easily done at this stage of the operation. At 
least 12 inches should be left between the outer air and the fine 
of active oxidation, and it is a good practical rule never to allow 
the surface to become so hot as to be unbearable to the naked 
hand. 

The too common practice of keeping the smelting department 
so far in advance of the ore supply as to require the breaking 
into and utilization of roast-heaps in which the ore is still red- 
hot, and just at the most active and profitable stage of calcina¬ 
tion, necessitates the employment of a strong body of laborers to 
bring water and constantly drench the smoking ore, in order to 
make it at all possible for the other workmen to shovel it into 
their barrows, and must be condemned as unnecessary and pro¬ 
ductive of more trouble and expense than almost any other prac¬ 
tice at our smelting-works. 

Among these sources of extra expense are the doubled cost of 
taking down and transporting the roasted material; the burning 
and rapid destruction of tools and cars; the medical bills claimed 
by the workmen who suffer from such unhealthy employment; 
and, far greater than all, the injurious effect on all subsequent 
steps of the process, which will be referred to in the chapter on 


Smelting in Blast-Furnaces. 

On the other hand, the only possible advantage that can be 
claimed is, that some two or three weeks’ interest on the value 
of the ore is saved. 

When the heap is properly cooled, the mass of ore, which, 
while still hot, is often almost as hard and tough as a wall of 
solid rock, crumbles to pieces with a single blow of the pick. 


78 MODERN AMERICAN METHODS OF COPPER SMELTING. 


and is wheeled in barrows from the roast-heap to the furnace- 
car. 

When the heap is sufficiently cooled, it is u stripped ” by re¬ 
moving* not only the fines that formed its cover, but its entire 
surface to such a depth as is necessary to include all material that 
has escaped oxidation. This unroasted material is made up 
largely of the fines forming the cover, and which, though often 
quite thoroughly oxidized on the top of the pile, are so aggluti¬ 
nated with sulphur as to be unfit for the furnace. The covering 
of the sides is seldom sufficiently roasted, and this is especially 
the case near the ground, where the ragging itself, to a depth of 
several inches, is frequently found unscathed. The angles of the 
pile are also seldom in good condition, and many isolated patches 
and bunches of ore will be found that the careful foreman will 
reject. This statement, however, refers rather to the results of 
the ordinary practice than to those that can easily be obtained by 
close attention to details and by enlisting the interest of some in¬ 
telligent foreman. As already explained, the fire will find its 
way to every nook and corner where sulphides still exist, if only 
the conditions are favorable. The author recollects with satis¬ 
faction the mortification displayed by his roasting foreman but a 
few months ago, at the unusual occurrence of a few hundred¬ 
weight of fused, and a still smaller amount of raw, ore in a heap 
of some 200 tons. 

A half-fused, honey-combed condition of the upper part of 
the heap, presenting the appearance of a skeleton of gangue from 
which all mineral has been melted out, is a certain indication of 
a proportional amount of matte below. This molten material 
naturally gravitates to the bottom of the heap, and is there found 
in masses of greater or less extent; often of many tons 7 weight, 
though, in such a case, warning would have been given during 
the roasting by the irregular sinking of the heap, and even by 
depressions and crater-like cavities on the surface. This molten 
product is very properly termed “ heap-matte,” and varies neither 
in appearance nor composition from the similar product of a 
blast-furnace. A popular impression prevails among certain fore¬ 
men, and even assayers, that the light honey-combed material 
that remains after the melting out of its sulphide constituents is 
rich in copper, but the contrary is true. The unfused skeleton 
merely represents the siliceous slag, while the molten sulphide 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


79 


mass below is the equivalent of the matte, the purity and value 
of either product depending* on the temperature to which the ore 
has been subjected, and the consequent perfection of the smelt¬ 
ing or liquidation process. This fact is sustained by the follow¬ 
ing assays of samples of considerable size: 


No. 1. 

Original ore before roasting. 21*6 copper. 

Siliceous skeleton. 7*3 “ 

Heap-matte. 34*7 “ 


No. 2.- 

18*6 copper. 
6*4 “ 


36*6 ‘ 


The formation of this heap-matte in any considerable quantity 
is very detrimental to the roasting process, but is easily avoid¬ 
able ; for it is invariably caused by either too much or too little 
air. In too many instances, no particular notice is taken of its 
occurrence, and it is sent to the smelting-furnace mixed with the 
well-roasted ore. This is exceedingly bad practice, and should 
on no account be permitted, as it is totally impossible to foresee 
the grade of matte that will be produced by the smelting process 
when this unroasted sulphide is mixed in unknown and varying 
quantities with the properly prepared charge. If the percentage 
of the furnace mixture be such that the addition of this raw 
matte does not lower the tenof* of the product below the desired 
standard, it may then, of course, be fed with the roasted ore, but 
should be kept strictly by itself, and added to each charge in 
weighed quantities. Any infringement of this rule gives rise to 
the formation of a matte varying greatly in its percentage of cop¬ 
per as well as in its entire composition, and deranges not only 
the smelting process, but seriously affects the regularity of the 
matte concentration operations. 

The heap-matte may occur in such masses that serious diffi¬ 
culty is experienced in breaking it up, especially as it retains its 
heat for a great length of time, and in this condition is almost 
malleable, yielding and flattening under the blows of the sledge 
like a block of wrought-iron. Much expense and annoyance may 
be spared by stripping the central molten mass thoroughly of all 
adhering ore, and allowing it to cool for two or three days; at 
the expiration of which time it will be found quite brittle and 
comparatively easy to deal with. Thorough and repeated drench- 
ings with water will produce even better results; but it should 
be borne in mind that a considerable proportion of the cuprifer¬ 
ous contents of calcined ore is in a soluble condition. 





80 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Wlien, through carelessness or inexperience, heap-matte is 
formed, it must be either treated together with the matte pro¬ 
duced from the first fusion in the blast-furnace, or set aside 
until a sufficient amount is collected to form a small heap by 
itself, and be re-roasted. It should, on no account, be mixed with 
the raw ore, as it demands a different treatment, and will either 
cause irregularities in the ore-roasting, or will pass through that 
process unaltered and with no perceptible diminution in its per¬ 
centage of sulphur. 

The proportion of strippings and other unfinished products of 
heap-roasting that may be considered allowable was determined 
experimentally by simply weighing the finished and unfinished 
portions of half a dozen consecutive roast-heaps, averaging about 
240 tons each. About 10 per cent, of fines were used for the 
covering layer in each case. The total amount of unroasted ma¬ 
terial, as given in the following table, shows that even a portion 
of the fines is thoroughly oxidized: 



Unroasted. 

Roasted. 

Days heap was 


Per cent. 

Per cent. 

active. 

No. 1. 

. 9-6 

90-4 

64 

U o 

. 6-6 

93-4 

71 

“ 3. 

. 8'-4 

9L6 

70 

“ 4. 

9-0 

91-0 

61 

“ 5. 

. 7*6 

92*4 

67 

“ 6. 

. 11*4 

88-6 

57 


The figures have been slightly corrected, without altering then- 
relative values, to make the aggregate in each case exactly equal 
100 per cent., which, of course, can never be precisely attained by 
adding the weights as actually arrived at. 

While these results are taken from ordinary every-day work, 
it should be understood that they can only be attained by the 
most careful attention in the roasting-yard. The proportion of 
-the product rejected as unfit for the smelting-furnace at some 
works might be even less than in the cases just cited, and the 
reason may be readily recognized in the low grade of the product 
from the fusion, and the constant complaints of the impossibility 
of keeping the matte up to the proper standard. A selection in 
such cases as rigid and thorough as in those just tabulated would 
result in the rejection of from 25 to 60 per cent, of the entire 
heap. An allowance of 10 per cent, may therefore be considered 
reasonable—although demanding more than ordinary care and 








THE ROASTING OF COPPER ORES IN LUMP FORM. 


81 


skill—and of this three-fourths should be fines. The stripping 
should be performed in a cleanly and systematic manner, and to 
an extent several feet in advance of the line of excavation, and 
the material thus removed piled on one side, to be subsequently 
screened on the first calm day; for the least wind causes a heavy 
loss when handling this half-oxidized powder. The fine part is 
again used as a covering, for which it is much better suited than 
raw ore, while the much smaller coarse portion is added to the 
nearest heap in process of erection. 

It will be readily seen that very much more fine ore is pro¬ 
duced during the processes of mining and crushing than can be 
used for the purpose of covering material, especially as only a 
small proportion of the latter is sufficiently oxidized at each 
operation to be passed on to the smelting-furnace. The problem 
of the best means of utilizing this constantly increasing amount 
of fine ore in works unprovided with calcining-furnaces is often 
a pressing one. It will be referred to again, under the heading, 
“ The Treatment of Pulverized Ores.” 

The roast-heap, when once tolerably cool, is torn down and 
loaded into the furnace-car with great celerity. Three or four 
men trundle the barrows, while double that number wield the 
pick, shovel, and hammer. It is the duty of these laborers to 
break all partially fused masses or lumps that are too large for 
proper smelting into fragments of a reasonable size, as especially 
determined by the metallurgists. There is not time, or space, or 
opportunity on the cliarging-floor of a blast-furnace in full opera¬ 
tion to attend to any duties beyond those immediately connected 
with weighing the charge and filling the furnace, and many serious 
irregularities in the smelting may be traced to an omission of this 
simple and obvious precaution. 

A careful and humane foreman can do much to mitigate the 
annoyance and suffering to which the workmen are subjected 
during the labor of tearing down a heap, by moving the point of 
attack from one to the other side of the pile, according to the di¬ 
rection of the wind, as well as by keeping the fresh surface on 
which the men are engaged well sprinkled with water, to settle 
the fine ore-dust. At best, this labor is the most disagreeable 
and wearing connected with ordinary smelting, and no laborer 
should be kept at such employment for more than three or four 
days in the week, and should be changed to some other task dur- 


82 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


ing the remaining time. Aside from the common tools already 
enumerated, long, stout steel gads and a few heavy sledges are 
needed to break up the central portion of the structure, which, 
although not fairly fused, is often so stuck together as to require 
considerable labor for its removal. At no other work are shovels 
so rapidly destroyed, and it is to this place that all partially 
worn, though still serviceable, tools are sent to terminate their 


existence. 

The tearing-down of the heap, and breaking-up of the matte 
that may be formed in it, are greatly facilitated by the use of a 
small quantity of dynamite, or other high explosives, selecting a 
powder of rather low force; containing not over 30 per cent, of 
nitro-glycerine. 

When this is properly used and in not too large quantities, it 
saves infinite labor with bar and pick, a single shot placed in a 
hole made in half a moment’s time with a bar, often accomplish¬ 
ing more than hours of hard labor. The shot should simply 
shake up and loosen the mass, leaving the large lumps to be 
broken up by sledge and pick, as usual. If enough powder is 
used to break the whole mass up into small fragments, a great 
portion of the ore will soar into the air and go toward top-dress¬ 
ing the surrounding country. 


I have never been able to get my men to be economical enough 
with their powder, excepting by forcing them to pay for it them¬ 
selves. When they realize that every penny that is saved on 
powder goes into their own pockets, it is astonishing how little it 
takes to do the same work that required several times the quan¬ 
tity when it cost them nothing. 

After the complete removal of the old heap and any slight re¬ 
pairs that may be required to restore the ground to its former 


level, a thin layer of raw fines is again spread on the old spot, 
and the fuel arranged for a fresh pile. The estimate of costs for 
this process, as given below, is based on the treatment of a very 

e- 

large amount of ores, varying greatly in composition, and under 
very various circumstances, and is purposely made somewhat 
liberal to allow for the occurrence of bad work and various other 
mishaps that are certain to occur in a greater or less degree. It 
is based upon a plant of 100 tons’ daily capacity, and on the as¬ 
sumption of only a short distance for transportation of the 
roasted ore to the smelting-furnace. 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


83 


ESTIMATE, 100 TONS PER 24 HOURS. 
Transportation to heaps, 2 men on car, weighing 1 man—3 men, at 


$1-50. $4.50 

Labor—building and burning heaps— \ 

4 men, at $1.50 = $6.00 [ 10.00 

2 men, at $2.00 = $4.00 ) 

Fuel at the rate of 5 cords per 24 hours at $5 a cord. 25.00 

Removing and loading roasted ore, 14 men at $1.50. 21.00 

1 foreman. 2.50 

Transportation to furnace and weighing (same as to heap). 4.50 

Oil, repairs to cars, track, etc. 3.25 

Miscellaneous labor, screening, daily patching, etc., 2 men at $1.50. 3.00 

Renewing shovels and other tools. 4.00 

Repairs on gads, bars, and tools. 2.75 


Total.$80.50 


Or 804 cents a ton of raw ore. On deducting the cost of the 
double transportation, as well as that portion of the labor belong¬ 
ing to the loading of the cars for the smelter, and for repairs to 
cars and track, etc.—none of which expenses actually belong to 
the process of heap-roasting as often estimated—the entire cost 
is at once reduced to 50 cents a ton, or thereabout. 

The various operations of heap-roasting may often be per¬ 
formed by contract to great advantage, especially if one has a 
good foreman to see that the quality of the roast is kept up to a 
sati sfactorv standard. 

To give an idea of the prices that are fair for this operation, 
I will mention what I paid for roasting a heavy, pyrrhotite ore 
in large quantities, say 150 to 200 tons per day, the climate be¬ 
ing excessively cold and stormy, and laborers’ wages about $1.40 
per 10 hours. The company furnished the wood for the roast- 
beds, and delivered the cars at the yard; but the cars had to lie 
unloaded by hand and the raw ore wheeled to the heaps, the 
arrangements for dumping the ore direct not having been then 
completed. 

For unloading the raw ore on the heaps, laying the wood, 
completing heaps, and covering and watching them throughout 
the entire operation, $0.22 per ton of ore. 

For stripping, tearing down, and loading the roasted ore on 
cars, and unloading the cars by hand into the smelter-bins, 
$0.16 per ton of ore. 

The contractors furnished their own powder, but the company 













84 MODERN AMERICAN METHODS OF COPPER SMELTING. 


provided tools, barrows, etc., though the contractors paid for the 
sharpening of their bars, picks, etc. 

On the above basis, the contractors made a fair profit when 
they attended strictly to their business, and when there were no 
interruptions or shut-downs. 

The degree of desulphurization arrived at by this process is 
seldom accurately determined, owing to the difficulty and expense 
of obtaining an accurate sample, and to the fact that the experi¬ 
enced eye can very correctly judge of the success of the roast, 
while any defect in the process will become immediately appar¬ 
ent in the lower tenor of the product of the succeeding fusion. 
Owing to the scarcity of accurate investigations on the subject, 
the following determinations w r ere made : 

No. 1. A heavy pyritous ore, from the Ely mine, Vermont, 
consisting principally of magnetic pyrites and clialcopyrite, 
burned in a heap of about 300 tons for eleven weeks. After 
stripping off the surface, a sample of the roasted ore, as delivered 
at the smelting-furnace, was taken. The following was the assay 
of the ore before and after calcination: 


Before roasting. After roasting. 

Sulphur.32’6 per cent. 7’4 per cent. 

Copper. 8'2 “ 9’1 “ 

Insoluble.27’0 “ 31*1 “ 


The condition of the copper in the roasted sample w r as also 
determined in this case, as follows: 

Sulphate of copper.1-3 per cent. 

Oxide of copper.2’1 11 

Sulphide of copper.5'7 “ 

Total.9-1 “ 

No. 2. A heavy pyritous ore, being almost pure iron pyrites 
containing minute quantities of copper, silver, and gold, from 
the Phillips mine, Buckskin, Colorado, was roasted for 6 weeks 
in piles of GO tons, and was used as a flux for siliceous silver 
ores. A careful sample of the roast yielded sulphur, before roast¬ 
ing, 464 per cent.; after roasting, 11 per cent. 

A considerable number of similar tests give corresponding 
results, showing that a very fair degree of desulphurization can 
be attained by this crude and ancient method, but still better re¬ 
sults will be reached in ores containing less pyrites, and making 










THE ROASTING OF COPPER ORES IN LUMP FORM. 


85 


the fact evident that, in heap-roasting as well as in the calcina¬ 
tion of pulverized sulphides, the copper is the last metal present 
to part with its sulphur, and that a large proportion of this still 
remains in the condition of a sulphide after nearly the entire iron 
contents have become thoroughly oxidized. This agrees per¬ 
fectly with all investigations relative to the comparative affinity 
of sulphur for the various metals, and is in no other metallur¬ 
gical process more strikingly exemplified than in the so-called 
“ kernel-roasting,” as practiced at Agordo, in Italy. There, the 
mechanical separation of the copper from its accompanying 
pyritous gangue is effected by stopping the process of calcination 
at the exact point where the entire iron contents have been oxi¬ 
dized into a soft earthy material, while the copper remains in 
combination with sulphur in a hard, metallic condition, and, most 
singularly, retreats into the center of each lump of ore, forming 
a heavy and solid kernel, which can easily be separated from its 
earthy envelope by inexpensive mechanical means. As this in¬ 
teresting process is not practiced in this country, and in all proba¬ 
bility is not suited to our domestic conditions, the student desir¬ 
ous of pursuing the subject will find in Plattner’s Rdstprocesse, as 
well as in a paper by the author in the Mineral Resources of the 
United States (A. Williams, Jr., 1883), further information. 

The appearance of a freshly-opened heap of well-roasted ore 
is characteristic, although difficult of description. It should 
present a strictly earthy, irregular surface of a blackish-brown 
hue, the scarcity of air preventing the oxidation of the iron to 
the red sesquioxide. This is a decided advantage in a reverbera¬ 
tory smelting-furnace, where the powerful carbonic oxide atmos¬ 
phere of the blast-furnace is wanting, to reduce it to the protox¬ 
ide, and thus fit it for entering the slag, the higher oxide being 
infusible at ordinary smelting temperatures. It is, in fact, prin¬ 
cipally a magnetic oxide, and, while the greater part of the con¬ 
tents should adhere closely together, and, when disturbed, should 
come out in the shape of large lumps, no sign of actual fusion 
should be visible, and the largest mass should fall into fragments 
at a few blows of the hammer. The more siliceous pieces of ore 
will have taken on a somewhat milky and opaque look in place 
of the ordinary vitreous appearance of quartzose minerals, and 
the veinlets of sulphides traversing the same will be found oxi¬ 
dized throughout. The solid lumps of pyrites, if carefully broken, 


86 MODERN AMERICAN METHODS OF COPPER SMELTING. 


will usually display a series of concentric layers, completely oxi¬ 
dized and earthy on the outside, and gradually acquiring greater 
firmness and a slight sub-metallic luster, which culminates in a 
rich kernel near the center of the fragment. This resembles 
strongly one or other of the grades of matte as produced from 
the smelting-furnace, and usually contains the greater part of the 
entire copper contents of the lump. The silver—if any be pres¬ 
ent—is also concentrated in a marked degree, though, so far as 
the author’s own investigations extend, not with the same re¬ 
markable perfection as the less precious metal. The examina¬ 
tion of a characteristic lump, such as just described, which con¬ 
tained before roasting about 4 per cent, of copper, yielded the 
following interesting results: 

The outer earthy envelope contained. Traces of copper. 

The medium concentric layers. 1'2 per cent. 

The central sub-metallic kernel. 69 ‘6 

An imperfect roasting is quickly detected by the presence of 
more or less fused material at certain portions of the heap, while 
elsewhere there exists no cohesion between the lumps of ore, 
which fall apart like so many paving-stones. A certain metallic 
appearance will also lie noticed, very different from the dull, 
earthy character of the properly burned pile. Although a large 
proportion of the contents may exhibit quite a brilliant red color, 
as though an unusually perfect oxidation of the iron had taken 
place, a mere weighing of one of the lumps in the hand will 
quickly undeceive the least experienced observer, and its fracture 
will show that the effect of the fire was only surface deep, while 
the entire interior remains unaltered. A careful study of differ- 
ent roast-heaps, wherever opportunity offers, wall soon render the 
student skillful in judging by eye of the degree of success at¬ 
tained by this process, and in after-life frequently furnish him the 
key to the cause of the unsatisfactory tenor of the matte pro¬ 
duced from his furnaces. No metallurgical process is more de¬ 
pendent upon an efficient and conscientious foreman, and the 
best results are usually obtained by selecting some intelligent 
and ambitious man from the roast-yard laborers, and holding 
him strictly responsible for results. 

A decided improvement in heap-roasting of ores was intro¬ 
duced at the works of The Canadian Copper Company of Sud¬ 
bury, Ontario, under the management of the author, in 1888-89. 





THE ROASTING OF COPPER ORES IN LUMP FORM. 


87 


It was first tried by his assistant, Mr. James McArthur, and 
proved so valuable that it became a regular practice under ordi¬ 
nary circumstances. 

W e have called it the u V-Method ” of roasting, and the accom¬ 
panying sketch will make it (dear. It consists in introducing a 
supplementary roast-heap between each two regular heaps, so 
that, if left untouched, there would be a continuous and unbroken 
roast-heap the entire length of the roast-yard. 

The supplementary heap should not be built until its two 
neighbors, which are to form its lateral walls, are well under way, 
and have been lighted from 10 to 14 days. By this time, if prop¬ 
erly managed, they will be cool enough on the outside to run no 
risk of setting afire the bed of wood which is laid down for the 
supplementary heap. The fresh bed of wood is laid down rather 
thinner than for independent heaps, and a single layer is extended 
well up the slope of the two neighboring heaps. The ore is 


No. I. No. 3. No. 2. 



dumped on as rapidly as possible, and the heap finished off with 
ragging and fines in the usual manner, and fired from the ends. 

The result is excellent, for the new heap, having its sides pro¬ 
tected, burns clear through its entire extent, and then sets on fire 
the still unroasted ore on the outside of the two neighboring heaps. 

Thus the proportion of unroasted ore is reduced to a mini¬ 
mum, and indeed is seldom worth keeping separate. 

Another great advantage is the economizing of space, for by 
this arrangement, some GO per cent, is added to the capacity of 
the roast-ground. 

It may require some little patience and experimentation at 
first to adapt this practice to a new ore, but it is well worth the 
trouble, and has been pronounced by the leading members of our 
profession, a decided and important improvement in this ancient 
and useful process. 

In the case referred to, the ore that was roasted was a nickelif- 
erous pyrrhotite mixed with chalcopyrite; but I have tried it 
sufficiently on both heavy and lean ores of the ordinary yellow 














88 MODERN AMERICAN METHODS OF COPPER SMELTING. 

iron pyrites to know that it is equally well adapted to all ores 
that are any way suited to lieap-roasting. 

HEAP-ROASTING OF MATTE. 

There remains only, in connection with this portion of the 
subject, to notice the slight deviations that it is found necessary 
to introduce in adapting this method to the treatment of matte. 

These artificially formed sulphides, containing variable per¬ 
centages of sulphur, may be sufficiently desulphurized in heaps, 
and their chemical composition has no marked effect upon the 
result, provided lead is not present to such an extent—fifteen per 
cent, or more—as to increase the fusibility of the material. 

The most marked distinction between the behavior of ore and 
matte, when submitted to this process, is, the fact that, while the 
former substance may be satisfactorily oxidized by a single treat¬ 
ment, the latter invariably demands two, and oftener three or 
more separate burnings before it is properly prepared for the 
succeeding fusion. There is no exception to this rule, which, if 
properly understood, would prevent the disappointment fre¬ 
quently experienced by those unaccustomed to this method of 
desulphurizing matte, and who are led to condemn the practice 
on finding, at the conclusion of the first carefully conducted 
burning, that the only visible results are a slight scorching of the 
surface of each fragment, a change in color from the original 
brownish-black to a brassy yellow, and a more or less extended 
fusion of such portions of the heap as have sustained the greatest 
heat. In reality, the influence of the process has been much 
more profound than can be realized from external appearances, 
and although neither the removal of the sulphur nor the oxida¬ 
tion of the iron and copper has progressed to any great extent, 
a certain change in the physical condition of every fragment of 
matte has been effected that prepares it perfectly for a second 
burning, and which seems a necessary preliminary to the actual 
desulphurization. 

Each succeeding operation requires a slightly increased pro¬ 
portion of fuel, as the volatilization of the sulphur and the oxi¬ 
dation of the metallic constituents deprive the matte of its in¬ 
ternal sources of heat, and at the same time greatly lessen its 
fusibility. 

For the first roasting, a bed of wood should be prepared simi- 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


89 


lar to that for a heap of ore, although smaller in area; for it is 
difficult to regulate the temperature and prevent matting in a 
heap much larger than twelve feet square, and this will be found 
a convenient size to hold from sixty to seventy tons of matte 
when raised to a height of about six feet. A single chimney in 
the center is sufficient, and about this structure the broken matte 
should be heaped just as it comes from the crusher or spalling- 
floor, and regardless of the fines that it contains. The presence 
of these has been found necessary to check the rapidity of the 
operation, and prevent the fire from suddenly spreading through 
the entire pile in a few hours without accomplishing any useful re¬ 
sult, though generating for a short time a temperature high enough 
to fuse a large proportion of the contents into a single lump. 

Less care need be taken in shaping a matte-heap than in the 
case of ore, and it is merely necessary to build it up in the form 
of a rude mound, which may best be covered with thoroughly 
burned ore from the roast-heaps, most of which on handling will 
crumble to a sufficient fineness for the purpose, while any hard 
lumps may be removed with the dung-fork. This obviates any 
screening or classifying of the matte in the open air, which al¬ 
ways entails a heavy loss, owing to the great value and excessive 
friability and lightness of the material after calcination. If, as 
is usually the case, the proportion of fines after the first burning 
is found so great as to endanger the proper combustion of the 
heap for the second operation, the mechanical loss may be re¬ 
duced to a minimum by separating the excess of pulverized matte 
by the use of a dung-fork, with tines closely set, during the turn¬ 
ing of the ore from the heap just finished on to the fresh bed of 
wood, and at the conclusion of the process, removing the fines 
that are thus isolated, either directly to the smelting-house, or, if 
they still contain too much sulphur, to the calcining-furnaces. 
The covering of the original heap, consisting solely of roasted ore, 
should be stripped off, and either sent to the smelting-furnace or 
again used for a similar purpose. It need hardly be mentioned 
that the presence of arsenic or similar impurities in the ore, in 
greater quantities than in the matte, should prevent any such 
practice as that just recommended, and it may be accepted as a 
universal rule in copper smelting, that- no impure ores or prod¬ 
ucts should ever be mixed with those freer from deleterious sub¬ 
stances. 


90 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Under no circumstances need a matte-pile be covered as 
thoroughly as a roast-heap consisting of ore, nor can the forma¬ 
tion of a considerable amount of matte, which in ore-roasting 
would be evidence of a great want of skill or care, be considered 
as a reproach, experience having so conclusively shown the im¬ 
possibility of preventing its occurrence that, unless about J of the 
lower portion of a matte-heap is thus fused, no thorough oxida¬ 
tion of the remainder will be effected. The time necessary for 
the operations just discussed varies according to the quality of 
the matte, the condition of the weather, and certain other factors,, 
but will in general be, for the first burning, eight days, while on 
the tenth day the heap wall be sufficiently cool to permit its turn¬ 
ing on to a fresh layer of fuel. The second operation requires a 
day longer, and the third a day less than the first burning. 

To those familiar with the practice of heap-roasting as applied 
to ores, no particular directions are necessary except that care 
should be taken that the large blocks of matte that are formed 
during each burning be well broken up and placed near the cen¬ 
ter of the heap next constructed, that they may have every op¬ 
portunity for a thorough desulphurization. Whatever raw matte 
still remains from the last burning is best reserved until the con¬ 
struction of a fresh heap furnishes the proper means for its treat¬ 
ment. At the last two burnings, it is well to introduce two or 
more layers of chips, bark, or other refuse fuel into the matte- 
heap 5 for it will act powerfully in decomposing the sulphates 
that at this stage are formed in considerable amount, and also ex¬ 
ercise a similar and most marked effect on whatever compounds 
of arsenic and antimony may be present. This simple measure 
had a sufficient effect in a certain instance in the experience of 
the author to be plainly noticeable in the quality of the ingot 
copper produced. 

No attempt to select such portions of thoroughly calcined ma¬ 
terial as will be found after the second burning has ever proved 
remunerative. The heap of matte must be treated as a whole, 
and the roastings continued until the desired grade of desul¬ 
phurization is reached. 

The process just described is seldom an advantageous one, as, 
aside from the production of the vilest fumes known to metal¬ 
lurgy, the value of the material operated on is too great to admit 
of being locked up for 30 days or more, or to warrant the loss 


THE ROASTING OF COPPER ORES IN LUMP FORM. 


91 


that necessarily results from such frequent handling in the open 
air. The last difficulty may be partially obviated by erecting a 
light structure to protect the heaps from the rain and wind; but, 
at best, the practice is an imperfect and objectionable one, and 
only to be recommended in new, outlying districts, where an ex¬ 
pensive calcining plant cannot at once be erected, and where the 
climate is favorable for out-of-door operations. The expense of 
crushing and calcining in furnaces is scarcely greater than the 
three or four burnings necessary to produce the same result; but 
the condition of the roasted material is so much more favorable 
for the succeeding smelting process, in the case of lieap-roasting, 
that this reason alone is often sufficient to outweigh all objections 
that can lie offered. 

The practice of spading the large pieces of matte upon the 
heap itself must be deprecated, as it has a strong tendency to 
solidify the structure and render the draught weak and irregular. 

The cost of this process, based upon the roasting of many 
thousand tons of matte, and divested of those details that too 
closely resemble the heap-roasting of ore to warrant repetition, 
is as follows, assuming the daily amount of fresh matte subjected 
to this treatment to average 30 tons: 


COST PER TON OF MATTE. 

First Fire. 

Breaking.$0.35 

Transportation to heap. 0.15 

Fuel—allowing 3 cords of wood to GO tons of matte. 0.25 

Constructing heap and burning. 0.32 

Total.$1.07 

Second Fire. 

Fuel—same as before with addition of chips.$0.30 

Turning heap and burning. 0.40 

Total.$0.70 

Third Fire. 

Fuel—same as second fire.$0.30 

Removing finished heap. 0.40 

Transportation to furnace and expense of preparing the 
raw matte still remaining, which results from the fused 
matte. 0.45 

Total.$1-15 

Total cost of 3 burnings.°...$2.92 



















CHAPTER V. 


STALL-ROASTING. 

At just what period in the history of the art it became cus¬ 
tomary to inclose the roast-heap with a little wall of earth or ma¬ 
son-work, in order to protect it against the elements, to concen¬ 
trate the heat, and to render unnecessary the tedious labor of 
covering the sides with fine ore, is unknown, though Agricola’s 
work on metallurgy shows that it was no novelty in the sixteenth 
century. These simple walls have since been heightened and 
sometimes connected with an arched roof; the area that they in¬ 
close has been paved and occasionally furnished with a perma¬ 
nent grate ; and, more important than all, the interior of the stall 
has been connected by a flue with a tall chimney, by which the 
draught has been improved, thus shortening the process of oxi¬ 
dation, while the noxious fumes are discharged into the atmos¬ 
phere at such a height as to render them unobjectionable in 
most cases. 

A very great variation exists in the size, shape, and general 
arrangement of stalls, hardly two metallurgical establishments 
building them after the same pattern, though all essential differ¬ 
ences may be properly considered by dividing them into two- 
classes : 

1. Open stalls, suitable only for ore. 

2 . Covered stalls, suitable for both ore and matte. 

1. Open Stalls .—Any attempt at an exhaustive description of 
the different patterns of ore-stalls that human ignorance, as well 
as ingenuity, has invented, would be a waste of space. They all 
consist of a comparatively small paved area, surrounded by at 
least three permanent walls, and usually having an open front, 
which is loosely built up at each operation, to confine the con¬ 
tents. The back or sides, or both, are pierced with small open¬ 
ings communicating with a flue common to a large number of 
stalls that enters a high stack. The draught is confined to these 


STALL-ROASTING. 


93 


passages by covering the surface of the ore with a layer of fines. 
From the great variety of existing patterns, one built at the 
works of the Parrot Copper and Silver Company, of Butte City, 
Montana, is selected for description as possessing exceptional ad¬ 
vantages as regards cheapness of construction, convenience of fill¬ 
ing and emptying, economy of fuel, and general adaptability. 

The stalls may be built either of common red brick, of stone, 
or, far better, of slag molded into large blocks, which, from their 
size and weight, require little or no extraneous support; while 
brick demands thorough and extensive tying together with iron¬ 
work, and stone of proper size and shape is expensive and is apt 
to crack when exposed to great fluctuations of temperature. 

As these so-called u slag-bricks ” are invaluable for walls and 
foundations, and in fact for every purpose for which the most 
expensive cut granite would prove available, and as they can be 
produced from almost any ordinary copper slag, a brief descrip¬ 
tion of the cheapest and best method of manufacturing them is 
appended. 

MANUFACTURE OF SLAG-BRICK. 

These are generally made from the slag of reverberatory 
smelting-furnaces, both because this material is usually more sili¬ 
ceous than any other, and also because, during the process of 
skimming, it can be obtained in large quantities in a very brief 
space of time. There should be no difficulty, however, in mak¬ 
ing the brick from the slag of a blast-furnace, provided the smelt¬ 
ing is sufficiently rapid to fill the molds properly, and that it is 
not so basic as to yield too fragile a material on cooling. Even 
with exceedingly brittle blocks, produced from a highly ferrugi¬ 
nous ore, excellent and durable walls can be constructed, provided 
the blocks are placed in position uninjured; for they will bear 
an immense crushing weight with impunity, and seem to defy 
the action of the elements. 

Assuming the slag to be obtained from a reverberatory fur¬ 
nace, the process of preparing the molds should be begun as soon 
as possible after the slabs from the previous skimming have been 
removed and all chips and fragments cleared from the sand bed 
by the aid of a close-toothed iron garden-rake. Ordinary loam— 

or a natural mixture of fine sand and clav of such consistence 

«/ 

that, when slightly moistened, it will ball firmly in the hand—is 


94 MODERN AMERICAN METHODS OF COPPER SMELTING. 

the proper material for the molds, which should he formed by 
means of a number of wooden blocks, of the required size, care¬ 
fully smoothed and slightly tapered to facilitate their removal 
from the sand, and furnished with a 30-incli handle, inserted in 
their* upper surface. These slag blocks are molded on the flat, 
in the same manner as ordinary red brick; and after leveling off 
the pile of dampened sand to form a smooth and horizontal bed, 
the wooden blocks—some twelve in number on each side of the 
skimming door—are arranged in a double row, four inches apart 
between blocks, and the same distance between the two parallel 
rows. 

Besides the ordinary deep excavation for the plate slag, a sec¬ 
ond bed should be left on each side, between the former and the 
first brick mold right and left, both for the purpose of settling 
any grains of metal that may be accidentally drawn over during 
the process of skimming, and to act as a regulating reservoir to 
lessen the sudden impulse of the waves of slag that follow each 
motion of the rabble, and thus to prevent the destruction of the 
very fragile sand molds. The entire bed is constructed on an in¬ 
clination of about one-half inch to the foot; the plate slag form¬ 
ing the summit, while the double row of molds slopes away from 
it in each direction laterally. After the wooden blocks have 
been placed on this sloping bed in a proper horizontal position, 
and exactly equidistant from each other, as determined by a 
wooden gauge, the remaining sand, very slightly but equably 
dampened, is shoveled back again, and carefully trodden and 
tamped evenly into all the interspaces and around the outside 
edges of the blocks, until it reaches the level of their upper sur¬ 
face. This is a very brief operation; for it is not essential to 
tamp the sand very firmly so long as about an equal degree of 
solidity is imparted to all portions of it. A cylinder of hard 

wood—three inches in diameter and four inches long—which, 

• 

when placed lengthwise, fits exactly between each two molds, is 
laid upon its side, and, by a few blows of the mallet, driven into 
the sand, thus when removed forming a, little gutter through the 
middle of the partition wall, and connecting each pair of adjacent 
cavities in such a manner that the flow of slag through either en¬ 
tire lateral system meets with no impediment. The wooden blocks 
are then removed from their sand bed with the greatest care, it 
often being necessary to loosen them by gentle tapping and other 


STALL-ROASTING. 


95 


means familiar to the experienced molder. The bed requires 
only a few hours’ drying to ht it for the slag. 

By the time the charge is ready for skimming, say in three 
hours or less after the completion of the bed just described, it 
should be in proper condition, and the furnace helper, armed with 
a small rabble-shaped hoe, stands beside the skimmer ready to 
turn the stream of slag into the proper molds, remove obstruc¬ 
tions from the gutters, break through the rapidly forming crust 
if indications of chilling appear on the surface of the molten bath, 
and see in general that the process of filling the molds proceeds 
in a proper manner. As soon as this operation is concluded, a 
few shovelfuls of sand should be thrown over the surface of the 
slabs to prevent sudden and unequal chilling. By the time the 
new charge is in the furnace and the assistant is at liberty to at¬ 
tend to his bricks, they will usually be found ready for removal, 
though still at a red heat on the surface and in most cases quite 
liquid in the interior. It is essential that they be removed, and 
the slight roughnesses that arise from the broken ends corre¬ 
sponding to the gutters through which they were filled be 
trimmed off with a small cutting hammer while they are still 
quite hot, as it is just at this stage that they possess the highest 
degree of toughness, and permit of manipulations that, if they 
were cool, would inevitably break them into fragments. These 
slabs are best removed from the furnace by being loaded upon 
the low iron barrow commonly used for the transportation of 
pigs of slag and matte. The loading is effected by means of a 
long five-eighths inch iron rod, bent into a hook at one end, and 
the blocks are then wheeled out upon the dump, where a special 
workman trims them properly, rejecting all that are imperfect or 
already cracked, and when cool, piles them into rows, to remain 
until needed. The most useful size for general purposes has 
been found to be about 8 by 10 by 20 inches, and weighing about 
85 pounds; but by simply changing the form of the pattern, they 
may be produced of any desired shape or size, although experi¬ 
ence has shown that it is not economy to attempt the manufact¬ 
ure of very thin slabs, or of any weight below 45 pounds. The 
immense value of this building material, produced from an other¬ 
wise worthless substance, and obtainable in rectangular shape for 
plain walls and foundations, in wedge shape for arches and for 
forming a circle in walling wells, and for many other daily needs, 


96 MODERN AMERICAN METHODS OF COPPER SMELTING. 

can be fully appreciated only by those who have had occasion to 
build in a country where rock was unobtainable and brick poor 
and expensive. 

A particular distinction should be made between the old plan 
of making- slabs of slag in iron molds, as practiced all over the 
world, and this method of sand molding, for which the profes¬ 
sion is indebted to Mr. J. E. Gaylord, Secretary of the Parrot Sil¬ 
ver and Copper Company. The author is well aware that mold¬ 
ing in sand has been practiced also, but never, so far as he knows, 

with such results as are obtained by the method indicated. 

*/ 

To return to the roasting stalls. Assuming that they are to 
be built of the material just described, and without any iron-work 

ROAST STALLS FOR ORE. 


CHIMNEY 



for anchoring, and that each stall is to burn a charge of 20 tons 
and be again cleared out in 10 days, thus furnishing 2 tons a day,, 
it will require some 56 stalls to furnish 100 tons of ore a day, al¬ 
lowing some 12 per cent, in excess of the needful capacity to per¬ 
mit of repairs. The weight of ore as brought to the stalls, and 
not as t alien from them, is counted: its loss during the process of 
calcination depends upon the quality and amount of sulphides 
present, and frequently reaches 15 per cent., though a consider¬ 
able portion of the loss in weight due to the elimination of the. 
sulphur is offset by the gain in oxygen. 

Such a battery of stalls should always be built in a double row, 
back to back, each lateral wall serving as the division between 






























































ROAST STALLS FOR OKt. 

SCALE % IN. = 1 FOOT 


STALL-ROASTING 


97 












































































































































































































98 MODERN AMERICAN METHODS OF COPPER SMELTING. 


the two adjacent partitions, while the unbroken rear walls form 
the sides of the main tine, a space of at least 2 feet being left be¬ 
tween them, which simply requires a 4-inch brick arch to form 
the main flue for the entire system. This also constitutes a foun¬ 
dation on which, after a little leveling up with earth, to prevent 
the sleepers from being affected by the heated masonry below, 
the narrow railroad is laid on which the ore for roasting is 
brought to any part of a given stall by means of the turn-plate 
and movable rails, explained in the chapter on Heap-Roasting. 
A double row of 28 stalls (56 in all) should have a flue at least 2 
by 4 feet for the third of the number nearest the chimney, which 
may be reduced to 2 by 3 feet for the middle, and 2 by 24 feet 
for the end third, if any saving can be effected thereby. The 
two long rear walls, inclosing the main flue, should be 32 inches 
thick—once and a half the length of a slag brick—with proper 
allowance for mortar and irregularities, and should be laid solely 
in clay mortar, which designation throughout this entire work 
may be understood to mean merely common sticky mud, such as 
is employed for making a poor quality of red brick. If ordinary 
clay be accessible, it may be mixed with sand in such proportions 
as to slip easily from the trowel: otherwise, any ordinary sticky 
mud may be used, and will be found to form perfectly satisfac¬ 
tory material for laying all mason work that is to be exposed to 
sulphur fumes and a heat not exceeding a dull red. 

The fact that lime mortar is totally unadapted to ordinary 
metallurgical uses, although doubtless universally known, is for 
some unaccountable reason frequently not acted upon, and the 
result in most cases is the rapid and total destruction of the 
furnace-arch, chimney, flue, or whatever structure may happen 
to have been put together with such unfit material. The acid 
vapors immediately form a sulphate with the lime present in the 
mortar, and this, absorbing water, becomes gypsum and crystal¬ 
lizes, expanding with great force, breaking the joints, and soon 
crumbles and washes away. It is quite proper to use lime mor¬ 
tar in such portions of the structure as are free from contact with 
heat and sulphurous gases, and yet require unusual strength, 
which cannot be obtained with the clay substitute. Such, for 
instance, as in the construction of chimneys for metallurgical 
purposes, where the best results can only be obtained by the em¬ 
ployment of both of these substances: lime mortar for the outside 


STALL-ROASTING. 


99 


work, while the common clay mud is merely used for the inside 
layer, and the joints thoroughly protected against any invasion 
of the sulphur gases by plastering the whole interior with a thin 
coating of clay mortar, tempered with sand to such an extent that 
it will not crack and fall off in sheets. Further reference will be 
made to this point in the chapter on Furnace Building. The con¬ 
stant and flagrant violation of this law is a sufficient reason for its 
frequent reiteration. A recent example suggests itself, where the 
arches of a number of very expensive and nearly new calcining- 
furnaces had fallen in, causing a very heavy loss. A conversa¬ 
tion with the mason who built them brought out the fact that 
they were constructed with lime mortar, he having had no or¬ 
ders to the contrary. 

The size of the stall is somewhat dependent upon the quality 
of the ore to be roasted, a highly siliceous ore with a compara¬ 
tively low percentage of sulphur permitting a much wider and 
higher stall than an ore with little gangue, and especially than 
one containing a considerable portion of iron pyrites, in which 
case extensive and unavoidable sintering will follow any attempt 
at increasing the size of the stall. A safe size for an average ore, 
containing a moderate amount of pyrite and demanding careful 
handling, is 8 feet in length by 6 feet in height by 6^ feet in 
width, the latter measurement being the maximum that is safe 
under any ordinary circumstances. It is best to build the lateral 
walls of the same thickness as the rear division, the increased 
stability and durability of the entire structure well repaying the 
slight additional expense in labor and material. The bottom 
should be paved with the same slabs placed flatwise and exactly 
reversed from the position in which they lay when formed; them 
upper surface now going downward, while their original lower 
surface, which should be perfectly smooth and level, now comes 
upward. The connection with the main flue is effected by means 
of 8 or 10 small rectangular openings—2 by (i inches—in the 
rear wall, in two or more rows, and at a considerable distance 
from the ground. These are kept tightly closed by means of a 
bunch of old rags or a ball of clay, when there is no occasion for 
their remaining open j otherwise, the draught of the entire sys¬ 
tem might suffer. 

The only air admitted to these stalls originally, at the Parrot 
works, came through such interstices as were left in roughly 


100 MODERN AMERICAN METHODS OF COPPER SMELTING. 


building’ up the temporary front wall; but experiments led to 
the addition of some 4 or 6 similar openings in each lateral wall, 
which did not communicate with the main culvert, but connected 
with the outside air by means of a small flue running longitudi¬ 
nally through each division wall, though not extending so far as 
the central passage. This innovation has been followed by a 
decided improvement in the oxidation of the ore and a great 
diminution in the amount of matte produced. An essential pre¬ 
caution in the management of these stalls is to maintain a thick 
coat of clay plastering over their entire interior surface, by which 
the heated ore is kept from sticking to the walls and causing the 
rapid destruction of the mason-work. A few moments’ attention 
to the empty structure after each operation will keep the plaster¬ 
ing intact and greatly lessen the cost of repairs. As the entire 
success of this process depends upon the strength and regularity 
of the draught, a stack of considerable size and height is essential. 

A battery of 56 stalls, as described, requires at sea-level a 
chimney 75 feet high, and with an internal area of at least 9 
square feet, as will be further explained in the chapter on the 
construction of calcining-furnaces. Any economy in the direc¬ 
tion of diminishing the size of this important adjunct will be im¬ 
mediately noticed in the lengthening of the roasting process, and 
may reduce the capacity of the stalls to an incredible degree. 
The draught is regulated by means of a sheet-iron damper hung 
in the main flue, close to its junction with the chimney, while the 
same office is accomplished for individual stalls by partially till¬ 
ing the draught-holes in the rear wall with bits of bricks or balls 
of clay. In no portion of the process, are the skill and care of 
the roasting foreman better displayed than in his management 
of the draught, which must be varied according to the season, 
and temperature of the air, as well as with the changing character 
of the ore. 

As already intimated, a stall of the size and pattern just de¬ 
scribed will hold about twenty tons of pyritous ore, which should 
be kindled with the very smallest possible quantity of wood that 
will set it thoroughly on tire. This is essential for a far more 
important reason than the mere saving in fuel • for the slightest 
increase in the contents of the bed of wood on which the rock is 
heaped will, with pyritous or otherwise easily fusible ores, cause 
an amount of sintering and a formation of matte entirely dispro- 


STALL-ROASTING. 


101 


portionate to the cause. Repeated trials can alone determine the 
various minutiae of this description essential to the best possible 
results with the material under treatment; but, in most cases, 
where the ore is at all pyritous, good sound wood will be found 
to produce too fierce a heat for the purpose, and recourse must 
be had to decayed wood, which can usually be obtained at from 
one-half to two-thirds of the price of the sound fuel. For an ore 
containing 30 per cent, sulphur and, say, 25 per cent, silica, 25 
cubic feet of rotten wood, or about one-fifth of a cord, will be 
found ample; but this small proportion of fuel—only one-hun¬ 
dredth of a cord to the ton—must be utilized in a proper manner, 
and with the most rigid economy and exactitude, or the heap 
will miss fire completely, doubling the cost of the operation, as 
well as interfering with the estimated production of the plant. 
A quarter of an hour spent in watching the manipulations of an 
experienced roaster is better than pages of description, though 
the operation of preparing a stall for its ore charge is far from 
complicated. 

After seeing that the layer of clay on the inclosing walls is 
renewed with the plastering-trowel where necessary, and that the 
draught-holes are open to the extent dictated by former experi¬ 
ence, a central longitudinal and two lateral flues are constructed 
on the floor of the stall out of large, irregular fragments of ore. 
These are merely to introduce air to the interior and to insure 
the rapid and thorough kindling of the entire structure. They 
are filled and surrounded with dry kindling-wood, and the 
greater part of the fuel, split into long, thin sticks from the large 
rotten logs and poles that are usually provided, is disposed in a 
thin layer over the bottom of the stall, the amount slightly in¬ 
creasing toward each side. The structure is now filled with 
coarse ore, and the ragging distributed throughout the entire 
contents rather than concentrated in a considerable layer merely 
upon the surface. As the stall becomes gradually filled, single 
small sticks of wood are placed between the ore and the lateral 
and back walls; while between the contents of the stall and the 
front wall, which is built up with large lumps of ore or stall 
matte, a considerable quantity of light wood is introduced to in¬ 
sure the thorough desulphurization of the anterior surface. A 
single car-load of ragging is spread on top of the coarse ore, and 
upon this a tliree-inch layer of shavings, bark, and chips is placed 


102 MODERN AMERICAN METHODS OF COPPER SMELTING. 

as a bed for about one and a half tons of raw fines, which, if dis¬ 
posed in the exact manner indicated, and covered thoroughly 
with well-roasted ore from a contiguous stall, will be thoroughly 
desulphurized, and the covering layer itself being in a well cal¬ 
cined condition, the entire contents, after burning, may be passed 
on to the next operation. Mr. R. Pierce, of Argo, uses with 
great advantage a sheet-iron cover over the top of his stalls, luted 
tightly with clay to the walls on which it rests. 

It is only by employing great care, and after repeated trials, 
that the requisite skill will be attained to thoroughly calcine the 
large proportion of fines just indicated; but when one reflects 
that it amounts to some seven per cent, of the entire ore, and per¬ 
haps one-half of the total fines produced, it will be seen that the 
result is worthy of any pains that can be expended on it. The 
large pieces of raw ore that are employed in building the flues 
and front wall become gradually oxidized upon the surface, and 
slowly crumble away and mix with the finished product until 
they totally disappear and are replaced by fresh pieces. When 
the ore is to be removed, the front wall is taken down, and the 
lumps of ore from it are piled out of the way, to be again used 
for the same purpose. 

The stall should be fired at night, as the smoke is so dense 
during the first few hours, and the draught so sluggish, that only 
a small part of the fumes find their way into the proper channel; 
but by the time the wood is consumed, the entire structure has 
become so much warmer as greatly to improve the draught. 
The sulphur and other products of volatilization and “sweating” 
—alluded to in describing the management of roast-heaps—form 
a sort of crust upon the surface, and seal all interstices connect¬ 
ing with the atmosphere, and force nearly all fumes to pass into 
the flue, thus greatly abating a nuisance. For the first twenty- 
four hours, the fire is confined to those portions of the ore that 
were in immediate contact with the fuel. The process of oxi¬ 
dation advances very rapidly, and by the close of the second day 
it is hardly possible to bear the hand upon the middle of the 
upper surface of the stall, showing that at least one-lialf the con¬ 
tents is already in combustion. By the end of the fourth day a 
similar degree of temperature may be felt upon the upper sur¬ 
face, at the very back of the stall, proving that the process has 
by that time invaded the entire length and breadth of the stall, 


STALL-ROASTING. 


103 


though considerable time is still necessary for its thorough com¬ 
pletion. 

The successful progress of the process is clearly marked by 
the great rise in height of the entire contents, gaining some 
three inches in a single day, and frequently ascending some 12 
inches above the level of the walls, at which it stood at the be¬ 
ginning of the operation, aside from the free space left to be filled 
out with ore from the disappearance of the fuel, amounting to 
some 25 cubic feet. This striking phenomenon, unfamiliar to 
those accustomed only to heap-roasting, where a settling rather 
than a rising of the entire mass occurs, is simply due to the fact 
that, m all cases of oxidizing roasting, a greater or less, though 
always very marked, increase in bulk occurs from the swelling 
and Assuring of the oxidized ore. The contents of the roast- 
heap, being perfectly free and unconfined, simply spread out lat¬ 
erally, while the consumption of the thick bed of fuel on wdiich 
it rests detracts considerably from its height. The walls of the 
stall, however, inclose the ore in a rigid grasp, making it abso¬ 
lutely necessary that any increase in bulk, beyond that very 
slight amount necessary to replace the space occupied by the fuel, 
should take place vertically. In a badly burned stall, where ex¬ 
tensive sintering lias taken place, and a sufficient amount of the 
sulphides has melted into a solid mass to cause a decided diminu¬ 
tion in bulk instead of an increase, the occurrence of crater-like 
depressions in the surface of the ore is positive evidence of such 
local fusions. That the pressure resulting from the increase in 
bulk is something quite tangible, may be inferred from the fre¬ 
quent pushing outward, or even overturning of the heavy lateral 
walls of a stall, provided one or the other of its contiguous com¬ 
partments is either empty or unbraced, while the temporary 
front wall would inevitably be thrown down within the first day 
after kindling if not strongly supported by timbers. 

The length of time necessary for the process under considera¬ 
tion is another uncertain factor. If the stall be left undisturbed, 
it will usually burn quietly for a period of twelve days, demand¬ 
ing little or no attention beyond an occasional shovelful of cover¬ 
ing if heating too fiercely at any one point, and requiring about 
three days additional to cool sufficiently to remove with comfort; 
but, under ordinary every-day circumstances, no such moderation 
can be practiced, and the period of each operation can be cur- 


104 MODERN AMERICAN METHODS OF COPPER SMELTING. 

tailed, without any especial damage, to one-half this time. To ac¬ 
complish this without detriment to the process of desulphuriza¬ 
tion, the following precautions must be adopted : As soon as the 
anterior surface of the ore is so cool as to impart no disagreeable 
sensation to the hand, the temporary front wall should be re¬ 
moved, the natural adhesion common to all sulphureted ores 
when roasted in lumps preventing the caving of the vertical ore 
face, which should be most carefully attacked with pick and 
shovel, every precaution being taken not to penetrate beyond the 
line of comparative cooling, and only so much ore being removed 
at any one operation as is consistent with the uninterrupted prog 
ress of the roasting in the mass behind. At least six or eight 
inches of ore should be left between the outer air and the line of 
fire, and any sudden elevation of the surface temperature, as well 
as increased difficulty in detaching the ore from the face on 
which work is prosecuted, is a sign to stop. To illustrate the 
ease with which the contents of a well-burned stall can be han¬ 
dled, the entire charge of ore from such a stall can be removed 
with nothing stronger than a shingle. 

The first car-load is usually taken from the stall at the close 
of the fourth day, and the amount capable of removal may be 
rapidly increased, until in seven days more the compartment is 
again empty. 

By this careful method of constant and systematic slicing, 
some two or three tons of well-burned ore may be taken daily 
from each of 40 or 50 stalls, and the capacity of the roasting 
plant rendered more than double what it would be if they were 
left untouched for the time necessary for their complete desul¬ 
phurization and cooling; while the process of oxidation does not 
suffer in the slightest degree if the precautions just enumerated 
are adhered to. 

In the case of ores containing arsenical pyrites, or, indeed, 
in the presence of any form of arsenical or antimonial combi¬ 
nations, a considerable proportion of the same that would other¬ 
wise go into the next operation in the shape of antimonates and 
arsenates may be volatilized and completely dispersed by the ad¬ 
mixture of chips, small coal, brush-wood or other carbonaceous 
materials, which, as in heap-roasting, exercise a powerful reduc¬ 
ing influence upon the products of oxidation just mentioned, and 
volatilize them m a metallic form. This simple precaution is of 


STALL-ROASTING. 


105 


much greater value in the calcination of similar compounds in a 
pulverized condition in furnaces, where the different periods of 
oxidation and reduction are under the control of the operator, 
and can he made to follow each other in the manner most con¬ 
ducive to the object in view; but even in the rude process under 
consideration, experience has shown, in many cases, that a de¬ 
cided improvement in the grade of copper has resulted from this 
device, the simplicity and economy of which are among its strong¬ 
est recommendations. 

The results obtained in stall-roasting vary little as compared 
with those from burning in heaps. On the whole, it is not quite 
so easy to prevent the formation of matte in the former practice, 
nor do average and oft-repeated examinations show quite as good 
results in the elimination of the sulphur. 

As circumstances may arise where it becomes the duty of the 
constructing metallurgist to decide between these two systems, to 
the positive exclusion of all methods involving the pulverization 
of the ore, and to give his reasons for and against each method, 
that his employers may also have some idea of the matter on 
which to base their advice or to rest the confirmation of his de¬ 
cision, it will be well concisely to review the comparative advan¬ 
tages and drawbacks of heap and stall-roasting* 

The first and most obvious advantage of the system of heap- 
roasting is the apparent cheapness and simplicity of the plant, 
only a level area being required, without furnaces, hues, stacks, 
or other expensive appurtenances. 

The extreme simplicity of the method and the very satisfac 
tory results obtained under proper management also speak in its 
favor; but further than this, no arguments can be advanced in 
support of the process. 

Even the economy in first cost of plant will be found more 
apparent than real, when the expense of the trestle-work and 
track, as well as the establishment of the different grades between 
spalling-slied, roast-yard, and smelting-house levels are considered, 
and no one will deny the absolute necessity for such an arrange- 


* See article on “The Mines and Smelting-Works of Butte City,” by the 
author, in the United States publication on Mineral Resources (by A. Will¬ 
iams, Jr., 1885). The third method of roasting lump ore—that is, in con¬ 
tinuous kilns—is only suited to certain peculiar conditions, and need not be 
considered when comparing the other two systems. 




106 MODERN AMERICAN METHODS OF COPPER SMELTING. 


inent if work on a large scale is to be prosecuted witli any degi ee 
of economy. 

A careful comparative calculation of costs, corrected by the 
results of actual work, shows that, under ordinary circumstances, 
the difference in cost between the two plants under consideration 
is too trifling to have much weight in the choice of methods, and 
may even be on the side of the stalls in cases where the natural 
conformation of the land is unfavorable for the establishment of 
the terraces necessary for cheap heap-roasting. 

A far more important reason for the adoption of the stall 
system is the great saving in time, by which the delay incidental 
to the cruder process of calcination is diminished by at least 
eighty per cent. 

In works of large capacity, this becomes a question of vital 
importance; for few smelting companies are so amply provided 
with capital as to carry a constant stock of some ten thousand 
tons of ore, representing a money value of several hundred 
thousand dollars, which is not at all an extravagant estimate for 
works of the capacity under consideration. The circumstance 
that this amount may be reduced to a sum not exceeding one-fifth 
of the above by the substitution of the quicker method of calci¬ 
nation is a weighty argument for its adoption. 

By a careful comparison of the expense of the two operations, 
we have already seen that a saving of about one-third may be 
effected by the use of stalls, owing principally to their greater 
economy in fuel and labor. 

A still further advantage may be claimed for them in the con¬ 
centration of all noxious fumes into a single flue, and their dis¬ 
charge into the atmosphere at such an elevation as to insure their 
gradual diffusion and dispersion without annoyance or damage. 
This is a great boon to the surrounding country, and more es¬ 
pecially to the workmen employed in the process of roasting, as 
any one familial* with the atmosphere of an establishment where 
heap-roasting is practiced can testify. 

Still further may be mentioned the considerable saving effected 
by the thorough roasting of the entire contents of the stall, in¬ 
cluding even the fine covering material, all of which is in con¬ 
dition for the succeeding operation ; whereas, in the case of heap- 
roasting, at least 10 per cent, of the entire stock requires a second 
handling. Here may also be considered the serious losses of 


STALL-ROASTING. 


107 


metal. from wind, rain, and other atmospheric causes, which, al¬ 
though not entirely obviated by the employment of stalls, are at 
least greatly lessened; the saving in a certain plant of moderate 
capacity amounting in a single year, according to the author’s 
calculations, to more than sufficient to cover the entire cost of 
erecting the stalls. 

But the most important advantage possessed by stall-roasting 
over heap-roasting in an ordinarily moist climate—if the process 
be carried on in the open air—is the prevention of loss by leaching. 

We have already pointed out the necessity of guarding against 
this loss by every possible means at our disposal; but even with 
every care a considerable loss from this source cannot be avoided 
in any ordinary climate. 

Mr. Wendt* gives some important figures bearing on this 
point, relating to heap-roasting as formerly practiced at Duck- 
town, Tenn., where, however, the rain-fall is exceptionally great. 
We quote also his estimates of cost, which, taking into account 
the low cost of fuel and labor, correspond closely with our own. 

u Ore-roasting, as thus carried out (in heaps), was a very 
economical process in point of labor and fuel. On an average, 
one cord of wood was consumed for 40 net tons of ore for each 
fire. The cost of labor in the first fire was 5 cents per 1,000 
pounds for both Mary and East Tennessee ores; for the second 
fire, 7 cents and 6 cents respectively were paid; and for fine ores, 
the pay was 12 cents per M. 

u The exact cost per net ton of ore was as follows: 


cord wood, at $3. $0.15 

Labor, 1st fire. .10 

Labor, 2d fire.14 

Materials.03 


Total per ton.$0.42 


u The losses of copper in the above-described roasting have 
been very generally ignored in judging of its expense. At least, 
proper emphasis has never been laid on them. 

“ Owing to an unexplained difference of several hundred 
thousand pounds between the fine copper produced at the Duck- 


* See The Pyrites Deposits of the Alleglianies, by A. F. Wendt. New York, 
1866, page 19. 











108 MODERN AMERICAN METHODS OF COPPER SMELTING. 

town smelter during a period extending over several years, and 
the monthly fine copper statements arrived at by deducting one 
and one-quarter unit from the assay value of the ores produced, 
the writer’s attention was forcibly called to this subject. A care¬ 
ful series of experiments was instituted; the results were rather 
startling. Repeated analysis of ore weighed into a roast-pile, and 
analysis and weighing of this same ore when sent to the matte 
furnaces, proved an almost incredible loss. 

“ From the large number of experiments and analyses,A quote 
the following striking examples: 


Pile No. 349.—Mary Ore. 


Gross weight of ore. 

Per cent, water. 

Per cent, copper. 

Fine copper, pounds. 

399,213 

2-5 

5-0 

19,461 

204,444 

95,182 

2*0 

5-8 

11,620 

3-8 

5-0 

3,617 

8,663 

3-0 

5-1 

428 

34,165 

6-0 

4-0 

1,284 


741,667 pounds raw ore contained 36,410 pounds copper. 


“The pile after roasting weighed 741,716 pounds—assayed 
3'31 per cent, copper—equivalent to 24,985 pounds fine copper; 
11,125 pounds copper, or 31’4 per cent, of the contents of the 
pile, had been lost while roasting; 170 days were consumed in 
roasting the ore, and 69 days in removing it to the smelting-fur¬ 
naces. Hence, the ore lay exposed to the weather for 239 days, 
that is, eight months. 


Pile No. 447.—Mary Ore. 


Gross weight of ore. 

Per cent, water. 

Per cent, copper. 

Fine copper, pounds. 

172,882 

3-0 

4-7 

7,881 

1,532 

5'5 

6-3 

91 

198,800 

2-0 

4-5 

8.767 

32,178 

4-0 

5-3 

1,637 

26,865 

5’5 

4-6 

1,167 

32,245 

3-0 

6-2 

1,939 


464,505 gross pounds ore contained 21,482 pounds copper. 


“Weight of the roasted ore was 495,566 pounds, assaying 
2*85 per cent., or 14,152 pounds fine copper. During an expos¬ 
ure of 186 days, the ore had lost 34‘3 per cent, of its copper. 


























STALL-ROASTING. 


109 


“All the experiments made on a total of nearly 3,000 tons of 
ore proved, beyond possibility of doubt, an average loss of more 
than one unit of copper, or over 20 pounds of ingot per ton of 
ore. This great loss during the roasting readily accounted for 
the deficit in the copper production, if only 11 per cent, was de¬ 
ducted from the assay value of the ores for losses by treatment. 
The actual loss by the smelting process, as practiced at Duck town, 
approached two units. Further experiments were made to con¬ 
firm the results obtained. Experiments in roasting in furnaces 
proved that no copper escaped in the fumes. This, indeed, was 
anticipated, as the heat in roasting never could reach a point at 
which copper is volatile. The only other possible loss is by the 
leaching of the roast-piles during the heavy rains frequent in the 
Ducktown hills; and to this cause the great losses were finally 
ascribed. In referring to experiments in the leaching of these 
ores later on, this subject will be discussed in detail. Suffice it 
here to say, that with a roasting in one fire only, from 1 to 1£ 
units of copper became soluble in water. The results were further 
confirmed by copper found in large quantity in the clay 4 bottoms ’ 
of the roast-piles. After a shower of rain, the roast-yard would 
be covered with pools of green water highly charged with copper/’ 

The cost of lieap-roasting was estimated at 80 cents a ton, 
including the transportation of the ore both to and from the 
roasting ground, as well as its weighing and other slight manipu¬ 
lations. The expense of roasting in stalls may be safely placed 
at 54 cents a ton, a figure based on the actual treatment of many 

thousand tons of ore by this method. 

«/ 

The cost of a battery of 56 stalls, built in the manner recom- 
mended, and reduced to the standard table of prices adhered to 
throughout this work, is appended. Their life, under ordinary 
treatment, will not exceed six years, at the expiration of which 
time they will be found in such a condition as to demand com¬ 
plete rebuilding, although, of course, the stack will outlast many 
generations of stalls. 

ESTIMATED COST OF 56 ROASTING-STALLS, EXCLUSIVE OF STACK. 

This being the first estimate yet given pertaining to the con¬ 
struction of any considerable portion of a smelting plant, the 
quickest and most convenient method of arriving at the desired 


110 MODERN AMERICAN METHODS OF COPPER SMELTING. 

result will be presented a little more in detail than may be con¬ 
sidered necessary in subsequent calculations. 

The total expense of the finished stalls may be conveniently 
divided into the following heads: 

1. Excavation for foundations. 

2. Cost of slag-brick, clay, and other building materials, de¬ 
livered on the ground. 

3. Labor in building the stalls. 

4. Total expense of the railroads belonging to this part of the 
plant. 

5. Miscellaneous expenses and superintendence. 

The actual expense of building a plant of this description will 
almost invariably be found much greater than the most carefully 
prepared estimates would indicate, unless the figures were made 
by a man of long experience in these matters. The value of the 
numerous estimates of cost and expense contained in these pages is 
principally due to the fact that they are, almost without excep¬ 
tion, taken from the results of actual work, executed under the 
superintendence of the author. They may, consequently, lay 
claim to a usefulness and reliability that the most carefully pre¬ 
pared estimates of cost would not possess unless derived from, 
or at least corrected by, a long and thorough personal experience 
in such matters. 

To prepare the foundations for the required number of stalls, 
assuming the ground to be comparatively level, will require about 
60 days’ labor, aside from the removal of the earth. This allows 
for an 8-inch pavement, and for an extension of the foundation 


walls about two feet under ground. 

1 . Excavation for foundations: 

Labor, 60 days, at $1.50.$90.00 

Removing the excavated material. 35.00 

Superintendence and miscellaneous extras. 32.00 

Total.$157.00 


In order to estimate the amount of building material required, 
it is essential to determine the cubic contents of all the walls in¬ 
closing the 56 stalls, 28 in each row. The stalls being 6J feet 
wide, and all walls being 32 inches thick, it will be seen that the 
entire length of the two main rear walls is 520 feet, to which 
must be added the aggregated length of the 58 partition walls, 







STALL-ROASTING. 


Ill 


each 8 feet long,=4G4, or a grand total length of 984 feet. This 
wall being G feet high and 32 inches thick, contains in round 
numbers 15,700 cubic feet. To this must still be added about 
one-third, to allow for the foundation walls, and also the neces¬ 
sary amount of slabs for paving the stalls. The details are as 
follows: 


Main walls.15,700 slag-brick. 

Foundation walls. 5,250 11 “ 

Paving. 2,080 “ “ 

Total.23,030 “ “ 

As these slabs are 8 by 10 by 20 inches, they contain very 
nearly a cubic foot each, and when the very coarse joints that 
they form are also considered, it will be found that their custom¬ 
ary rating of a cubic foot each will be perfectly safe. They are 
laid entirely in ordinary clayey loam, which may be found almost 
everywhere, and which, if too sticky to leave the trowel, will be 
greatly improved by the addition of one-fourth or more of sand, 
or even sandy loam. At our standard of prices, $1 per ton will 
be ample for such material, and will lay one hundred brick. The 
cost of the slag-brick has been placed at two cents on the ground, 
as their delivery is at least as expensive as their manufacture. 
The sum mentioned, that is, two cents apiece delivered, or one 
cent at the furnace, will cover the cost of making and trimming, 
and leave enough margin to occasionally replace the pattern 
blocks and other material necessary for their production. 

2. Cost of materials for mason-work: 


23,000 slag-brick, at 2 cents.. .$460.00 

235 tons clay, at $1. 235.00 

Mortar-boxes, hods, screens, etc. 45.00 


Total.$740.00 


The persons employed for this work should on no account be 
the regular, high-priced brick-masons, as these fare but badly in 
handling the heavy, brittle slabs, and neither like the work nor 
are able to earn the large wages that they invariably demand 
and receive. The proper mechanics for this work are what are 
popularly known as “ country stone-masons,” whose apprentice¬ 
ship at building stone walls, underpinning barns and houses, etc., 












112 MODERN AMERICAN METHODS OF COPPER SMELTING. 


lias exactly prepared them for handling such rough and heavy 
material as that under discussion. 

Experience in this particular kind of construction has shown 
that the most advantageous distribution of the force is to provide 
each stone-mason with two immediate helpers, who assist him 
constantly, bringing the slab, placing it in position, and, in fact, 
doing everything excepting the spreading of the mortar and that 
last wedging and chinking that are of such vital importance in 
the proper execution of work of this description. 

There are no liod-carriers, as the slabs are delivered by wag¬ 
ons at the point most convenient to the workmen, and the mor¬ 
tar, easily and rapidly manufactured from the materials already 
mentioned, is brought in large pails, being used in immense 
quantities in work of this description, although every crevice 
should be well filled with small fragments of rock or slag, called 
“ spalls.” 

It has been found that each group of three men, as described 
above, will lay on an average 100 slag-brick daily, and not more. 

3. Labor in building stalls : 


Estimate for laying 100 brick: 

One stone-mason.$3.00 

Two laborers at $1.50. 3.00 

Mixing mortar for same.50 

Carrying mortar and other miscellaneous labor.15 

Superintendence.35 


Total for 100.$7.00 

Total for 23,000 brick.$1,610.00 


4. Cost of railroad tracks .—As all railroads about the works 
should be of the same gauge and pattern, a single detailed es¬ 
timate will determine the cost per foot once for all. For tracks 
of the required description, having a 22-inch gauge, and calcu¬ 
lated to carry a net load of 1,800 pounds, the car weighing an 
additional 800 pounds, a good quality T-rail of not less than 12 
pounds to the yard should be selected and well fastened in place 
by a spike in every sleeper, while the abutting ends of the rails 
should be firmly secured by fish-plates, tapped for four f-ineh 
bolts, two to each rail. Unless the bolt-holes in both fish-plates- 
and rails can be bored where ordered in such a manner that 
there shall be no doubt of their perfect correspondence, it is- 










STALL-ROASTING. 


113 


better to leave the plates blank, and bore them on the spot. This 
may seem a slight matter, but its neglect sometimes causes seri¬ 
ous annoyance and delay in outlying districts, and the boring of 
the thin fish-plates is a slight task, as every smelter should be 
provided with a boring-machine run by power, which is indispen¬ 
sable for sampling pig-copper, and will be found generally useful. 

The sleepers are sawed from the ordinary timber of the coun¬ 
try, and may be conveniently ordered of the following dimen¬ 
sions : 36 inches long, 6 inches wide, and 4 inches thick—con¬ 
taining each 6 feet, board measure. They should be placed 39 
inches apart from center to center, and last almost indefinitely, 
as the sulphate salts with which they become impregnated pre¬ 
vent their decay. 

«/ 

For convenience of calculation, the estimate will be based on 
a length of 100 yards of track: 

Weight of iron : 

200 yards rails at 12 pounds = 2,400 pounds 

Spikes, bolts, and fish-plates = 115 11 

Total.2,515 pounds x 3| cents = $88.02 

Sleepers: 

125 containing 6 feet each = 750 feet at $25 per M = 18.75 


Labor : 

Grading, laying track, ballasting, etc.$13.50 

Superintendence. 6.00 


Total. 19.50 

Average allowance for curves and switches. 13.63 

10 per cent, for incidentals. 14.00 


$153.90 


We may therefore accept the figure of $1.53 per yard, or 51 
cents per foot, as the cost of a tram-road of this description, and 
there being three lines of track required for the stalls, aggregat¬ 
ing a length of 780 feet, to which must be added 100 feet for con¬ 
nections, switches, and single main line to smelter, we have a 
total of 880 feet at 51 cents = $448.80. 

Rails for long curves may be bent cold; for short curves, they 
must be slightly heated ; while frogs, points, etc., require welding, 
and can be readily constructed in any ordinary blacksmith’s 
forge. 

Great care should be taken in laying the track, nor should 











114 MODERN AMERICAN METHODS OF COPPER SMELTING. 


the foreman rest satisfied until every point, frog, and guard rail 
is in proper position and has the precise curve necessary for easy 
passage of the car without undue friction or danger of derail¬ 


ment. It is scarcely necessary to say that this work can only be 
properly and economically executed under the direction of an 
experienced railroad constructor. 


5. Miscellaneous expenses and superintendence .—Aside from 
the allowance made in each department of the work for the 
above purposes, it will be found in practice that a considerable 
additional sum is required to cover errors in construction, black¬ 


smith work, and various incidentals, as well as general superin¬ 
tendence, amounting in a case similar to the above to 


$211.00 

Cost of 4-inch brick arch to cover main flue. 137.00 

$348.00 

Summary. 


Excavation for foundations. $157.00 

Materials for mason-work . 740.00 

Labor in building stalls.1,610.00 

Railroads. 448.80 

Miscellaneous and superintendence. 348.00 


Grand total.$3,303.80 


Uneven ground, bad weather, and other unfavorable causes 
may increase this sum to a considerable extent, but the figures 
given will be found safe under ordinary circumstances and with 
strictly judicious and economical management. 

The calcination of matte in ore stalls of the pattern just de¬ 
scribed is by no means impossible, the principal difference be¬ 
tween its treatment and that of ore being the increased quantity 
of fuel required—about three times as much. A considerable 
proportion of the matte will be fused during the operation, and 
another large fraction scarcely affected by the process; so that 
from three to four burnings are required to effect any reason¬ 
ably perfect desulphurization. 

This practice cannot be recommended, as much better results 
are obtained by providing the stalls with grate-bars, and prevent¬ 
ing the radiation of heat from the surface by means of an 
arched brick roof, as described in the succeeding chapter. 












STALL-ROASTING. 


115 


THE STALL-ROASTING OF MATTE. 

This is a method well known in the Eastern States, and prac¬ 
ticed first in this country, so far as any record can be found, at 
the old Revere Copper-Works in Boston, and in more modern 
times at Copperas Hill in Vermont, and at the noted Vershire 
mine in the same State, where some sixty or seventy stalls are 
still in use. The partial suppression of the excessively disagree¬ 
able fumes generated in the lieap-roasting of this substance; a 
gain of at least one-third in the time of treatment—no unimpor¬ 
tant item in the handling of such valuable material; and a very 
great diminution in the losses caused by the elements, are the 
principal reasons for the selection of stalls in preference to heaps. 
On the other hand must be placed a heavy investment in build¬ 
ings and in the stalls themselves, with their flues, stacks, etc. 
The mere grate-bars for a single matte stall cost in the neighbor¬ 
hood of $75, and the constant repairs that are peculiarly neces¬ 
sary in the case of mason-work saturated with the products of 
volatilization, and racked by the frequent and extensive fluctua¬ 
tions in temperature, due to the ever-recurring heating and cool¬ 
ing of the interior, render them a somewhat expensive portion 
of the plant, as will be seen in detail in its proper place. 

MANAGEMENT OF MATTE STALLS. 

The grate-bars being thoroughly cleansed and freed from all 
clinkers and debris of the preceding operation, and replaced in 
position, and the brick walls forming the sides and back of the 
stall receiving a fresh coat of plaster (clay) where necessary, a 
layer of fuel is placed upon the grate-bars, and the broken matte 
thrown upon this by means of a closelv-tined fork, to separate 
the fine stuff, which is scattered over the top after the stall is 
filled with an average charge of from five to six tons. 

The fuel employed is wood in 4 or 6-foot, lengths, and split to 
a comparatively uniform size. From 10 to 20 cubic feet are used 
for each charge, metal of low grade rich in sulphur requiring 
less fuel than the higher varieties of matte. Experience has 
taught the great advantage obtained by the use of hard wood, 
and too much care cannot be bestowed upon the selection of the 
fuel, which should be of the best quality and thoroughly sea- 


116 MODERN AMERICAN METHODS OF COPPER SMELTING. 

soiled, as the result of the operation depends to a remarkable ex¬ 
tent upon the quality of the fuel used. 

Matte of any grade, from the lowest coarse metal to the high¬ 
est quality of regule, may he treated in these stalls with almost 
equal results as regards desulphurization. 

The stalls are always covered by rude sheds, to protect the 
brick-work from the weather, and should be paved with slag 
blocks, flat stone, or, much better, heavy iron plates, as the con¬ 
stant hammering that it must undergo during the spalling of the 
matte and the breaking of the huge clinkers that form an almost 
necessary accompaniment of this process, quickly destroys any 
other description of pavement. 

The results of desulphurization by this method being no more 
thorough than by heap-roasting, the same number of burnings is 
necessary as in the latter case, and, owing to the difficulty of re¬ 
moving the heavy clinkers from the walls and grate-bars of these 
little furnaces, as well as the constant bill of expense for repairs, 
the cost of the process is about the same as in heap-roasting. 
The almost complete identity of the two methods in this respect 
renders any further details of expense unnecessary. 

The imperfections of all the methods of roasting matte in 
lump form, as well as the great waste of time and metal, and the 
annoyance caused by the fumes, are serious objections, and it is 
only under exceptional circumstances that these crude and dila¬ 
tory methods can be recommended. In nearly all advanced 
works, they have given place to the much more rapid and perfect 

method of calcination in reverberatorv furnaces. 

«/ 

The orclinarv dimensions of the stalls in use, now or formerlv, 
at some of the principal works in this country are as follows: 


Width..5 feet. 

Depth (front to back).6 feet. 

Depth of ash-pit. 1 foot 6 inches. 

Height from grate to spring of arch.4 feet 8 inches. 

Thickness of division walls.1 foot 4 inches. 

Thickness of rear walls.1 foot 8 inches. 

Area of flue opening in rear wall.160 square inches. 


A stall of this size will contain from five to six tons of matte, 
and will burn for four days at the first firing, and for about three 
days at each subsequent operation. 

Where three burnings take place, the capacity of each matte 









STALL-ROASTING. 


117 


stall may be placed at one-half ton daily, and the amount of 
wood required for the three burnings will be one-twelfth of a 
cord per ton of ore. 

From the measurements already given, aided by the estimates 
for brick-work found in a succeeding chapter, the cost of a block 
of such covered stalls may be easily arrived at; the covering arch 
consisting of a 9-inch semicircle of red bricks, and the main flue 
section being at least equal to the combined area of the flues that 
enter it. 

The anchoring of a block of such stalls is very simple, con¬ 
sisting of longitudinal f-inch rods, while the uprights may be 
iron rails or stout wooden timbers. Each side wall should also 
be braced from front to back in the usual manner, while the 
front wall of the stall is a temporary structure of brick laid 
loosely upon the grate-bars and braced with a few lengths of flat 
iron. Fire-brick are ordinarily used for this purpose, the com¬ 
mon red brick of which the entire permanent portion of the 
structure is built being too light and fragile to stand the repeated 
handlings and the fluctuations of temperature. 

Since the ordinary charge only fills the stall about two-thirds 
full at the front, and slopes up against the rear wall to nearly 
the height of the flue opening near the top of the walls, or even 
in the arched roof, a large space exists between the upper edge 
of the temporary front retaining wall and the high semicircular 
brick roof. Through this, the sulphurous fumes and the prod¬ 
ucts of the combustion of the fuel during an early stage of the 
process escape in such clouds as to render the atmosphere of the 
shed unfit for respiration. To partially obviate this difficulty, a 
sheet-iron curtain, suspended by wires running over a pulley in 
the roof, and furnished with a counter-weight, is used, and if 
properly fitted and luted to the side walls with a paste of stiff 
clay, is of great service. 

It may be assumed with safety that, by the process of matte- 
roasting in lump form—whether executed in heaps or covered 
stalls—from two-thirds to three-fourths of its original sulphur 
contents is eliminated, by not less than three consecutive burn¬ 
ings. 


CHAPTER VI. 


THE ROASTING OF ORES IN LUMP FORM IN KILNS. 

By the term kiln, as used here, we understand a compara¬ 
tively small, shaft-like furnace, provided with a grate or opening 
for the admission of air from the bottom, and connected with a 
draught flue. The action is a continuous one, and the necessary 
heat is derived entirely from the oxidation of the sulphur and the 
other constituents of the ore. 

No other class of furnaces has received greater attention or 
been brought to a greater state of perfection; but it is as an ad¬ 
junct to the manufacture of sulphuric acid rather than to the 
calcination of ore that this apparatus must be esteemed, and con¬ 
sequently to the works treating on that subject that we must look 
for detailed descriptions and estimates of the same. The student 
is referred to Lunge’s exhaustive work on Sulphuric Acid for full 
details of construction and management. 

While the various processes of roasting hitherto described are 
suited to almost every variety of sulphureted copper ore, and 
yield equally good results whether the percentage of sulphur and 
copper is small or large, a much closer selection of material is in¬ 
dispensable for successful roasting in kilns, and then* range of 
usefulness is restricted to comparatively narrow limits. 

This very question of selection, however, varies greatly with 
the purpose in view, and depends upon whether it is desired 
merely to desulphurize a given ore without any attempt to utilize 
the volatile products of oxidation, or whether the manufacture of 
sulphuric acid is to be combined with the process of roasting. 

The conditions necessarily present before any pyrites can be 
utilized for the manufacture of sulphuric acid are of two kinds, 
commercial and technical. 

The commercial conditions are sufficiently obvious to any 
thoughtful mind, and are very plain, such as sufficient supply of 
ore at a fixed and low rate for a reasonable length of time, and 
contiguity to water, railroads, or some cheap means of transpor- 


119 


THE ROASTING OF ORES IN LUMP FORM IN KILNS. 


tation to the manufactory, which, owing to the nature of its prod¬ 
uct, must be situated in the immediate vicinity of its market. 

The technical conditions, though more numerous, are almost 
equally easy of comprehension. An almost absolute freedom 
from gangue is essential, for the simple reason that the presence 
of foreign substances lowers the percentage of sulphur and neces¬ 
sitates the handling of worthless material, thus lessening the ca¬ 
pacity of the works and producing other unfavorable results. 
For the same reason, though in a less degree, the presence of any 
other sulphides but the bisulphide of iron, which forms the ore 
proper, is disadvantageous; for no other compound of sulphur 
contains either so high a percentage of the same or parts with it 
so freely. Even the copper pyrites, which in many instances 
forms the principal value of the ore, is detrimental to the manu¬ 
facture of sulphuric acid, both because it contains less sulphur 
and because it is too fusible to permit the proper regulation of 
the temperature. Beyond the limit of eight per cent, of copper 
in the pyrites, it cannot be profitably employed in the manufact¬ 
ure of acid. The Spanish pyrites, from which so large a propor¬ 
tion of the acid produced in England is made, contains on an 
average about three per cent, of copper, and about 48 per cent, 
of sulphur, this remarkably high percentage of sulphur showing 
its freedom from gangue. 

An analysis of the. average ore from the celebrated Rio Tinto 
mine may be of interest, as a type of a very favorable cupriferous 
pyrite for acid making: 


ANALYSIS OF RIO TINTO PYRITES BY PATTINSON. 


Sulphur. 48‘00 

Iron. 40'74 

Copper . 3'42 

Lead. 0'82 

Lime. 0'21 


Total 


Magnesia. 

Arsenic.. 

Insoluble.. 

Oxygen and moisture 


0'08 

0'21 

5'67 

1'00 


100'15 


The ore used by three large acid-works in Boston and New 
York is obtained principally from Canada, some thirty miles 
from the Vermont fine, and although somewhat variable in 
purity, averages about 3*5 per cent, of copper and 45 per cent, of 
sulphur, the percentage of gangue being greater than in the 
Spanish ores. 

An excellent quality of pyrites is mined from a large deposit 














120 MODERN AMERICAN METHODS OF COPPER SMELTING. 

in Western Massachusetts, and in both Virginia and Georgia are 
beds of pyrites now under process of development, which, on 
•competent authority, are said to rival the Spanish mines in 
almost every particular. The total product of pyrites for the 
United States in 1890 was 97,706 tons. There were also 115,000 
tons imported from foreign countries, principally from Spain. 

The presence of arsenic and antimony has a deleterious effect 
on the quality of the resulting acid, while lead heightens the 
fusibility of the charge, besides wasting sulphur by forming a 
stable lead sulphate, and any foreign substance, however harm¬ 
less otherwise, lessens the percentage of sulphur. 

An important point, sometimes overlooked by non-profes¬ 
sionals in determining the value of a sample of pyrites, is its me¬ 
chanical behavior during the process both of crushing and of roast¬ 
ing. A granular ore, soft or easily disintegrated, will increase the 
proportion of fines, which, although now utilized with great suc¬ 
cess in the manufacture of acid, are still undesirable as requiring 
a more expensive plant and entailing a greater cost in their treat¬ 
ment. A still more serious production of fines may take place in 
the kiln itself in the case of ores that decrepitate, sometimes 
occurring to such an extent as entirely to choke the draught and 
render their employment impossible. 

One of the most serious errors ever perpetrated in the manu¬ 
facture of acid from pyrites is the attempted employment of 
pyrrhotite or monosulphide of iron for pyrite—bisulphide of 
iron. Aside from the greatly lessened proportion of sulphur, 36 
per cent, as against 53 per cent., the monosulphide will not even 
yield freely what sulphur it contains, but crusts with oxide of 
iron, turns black, and is soon extinguished when treated in an 
ordinary pyrites kiln. It seems scarcely possible that extensive 
works for the manufacture of sulphuric acid (and copper) should 
have been erected, their ore supply being entirely derived from a 
deposit of the valueless monosulphide; but such has been the 
case in more than one instance, and will continue to be so in en¬ 
terprises conducted without the aid of skilled direction. One of 
the most striking instances of this kind is a now extinct Massa¬ 
chusetts company, which is said to have expended over $200,000 
in this manner, all of which was a total loss, excepting the small 
amount realized from the sale of buildings and lands. 

Under certain conditions, the use of kilns for the calcination 


121 


THE ROASTING OF ORES IN LUMP FORM IN KILNS. 

of cupriferous pyrites without the production of sulphuric acid 
may be found advantageous, as in the case of the former Orford 
Nickel and Copper Company, near Sherbrooke, Province of Que¬ 
bec, which, after employing heap-roasting for some time, erected 
a large number of kilns solely for the purpose of calcining its ore 
previous to smelting; finding the saving in time and avoidance 
of waste, combined with the lessening of the annoyance formerly 
experienced from sulphur fumes, a sufficient advantage to repay 
the somewhat heavy cost of the burners. 

The minimum percentage of sulphur sufficient to maintain 
combustion in kilns does not yet seem to have been positively de¬ 
termined ; but with an ore otherwise favorable, it is probable that 
25 per cent, is quite sufficient for the purpose. 

For economy’s sake, as well as for the purpose of retaining 
the heat, kilns are constructed in blocks of considerable length, 
and of the depth of two burners, the front of each facing out¬ 
ward, while the flue in which the gas is conveyed to its destina¬ 
tion is built on top of the longitudinal center wall. Fire-bricks 
are used wherever the masonry is exposed to heat or wear, and 
the entire block of furnaces is surrounded by cast-iron plates, 
firmly bolted in position, and provided with the necessary open¬ 
ings for manipulation. 

No fuel is required after the burners are once in operation; 
and when in normal condition, the attendance demanded, aside 
from the labor connected with the regular charge of from 500 to 
2,000 pounds of ore once in twelve or twenty-four hours, is very 
slight. 

Much skill and experience, however, are required to maintain 
the regular working of the kilns, especially with ores that are not 
exactly suited to the process. 

From five to ten per cent, of fines may also be desulphurized 
with the coarse ore without seriously interfering with the process. 
They are thrown toward the back and sides of the shaft, leaving 
the center uncovered; otherwise, the draught is affected and seri¬ 
ous irregularities supervene. 

In accordance with the policy adopted throughout this work, 
no detailed estimate of expense will be given in the few instances 
where the author is unable to base the same on personal experi¬ 
ence. 

Such is the case in kiln-roasting • but we are assured by the 


122 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


best authorities that the expense of calcination by this method 
does not exceed that of stall-roasting, though the first cost of the 
plant is considerably greater. 

The results obtained by this process are unexampled in the 
roasting of lump ores, although there is no doubt that a consider¬ 
able share of the success is due to the fact that the sulphur is the 
object of interest, instead of merely being a waste product to be 
driven off as far as convenient. 

If more than 4 per cent, of sulphur remains in the cinders , as 
the residue from this process is called, the result is not considered 
satisfactory. It is needless to say that such a perfect desulphuri¬ 
zation cannot be obtained in either heap or stall-roasting, nor is 
it necessary or, in many cases, even beneficial for the subsequent 
process, although, of course, in most instances the lack of sulphur 
in the furnace charge forms a welcome outlet for the’admixture 
of raw fines, which may thus escape the expense of calcination. 

Within the past few years, the utilization of these fines lias 
attracted much attention, and the efforts to calcine them in au¬ 
tomatic furnaces for the production of sulphurous acid have been 
crowned with success, as will be again alluded to when treating 
of the Roasting of Pulverized Materials. 

The attempt to utilize kilns, with certain slight modifications, 
for the roasting of copper matte has, after many difficulties and 
much expense, attained a successful issue at certain European 
works, especially at the Mansfeld copper-works in Germany, the 
object in view being rather the abolition of the nuisance arising 
from the escape of the sulphur fumes into the atmosphere than 
any expectation of financial advantage from the employment of 
a substance so poor in sulphur for the manufacture of acid. It 
is obvious that only mattes comparatively free from lead and 
other fusible metals can be treated in this manner, and that the 
process of roasting is beset with difficulties that have only been 
overcome by the exercise of the greatest skill and patience. 


CHAPTER VII. 


CALCINATION OF ORE AND MATTE IN FINELY DIVIDED CONDITION. 

Perhaps the most marked point of difference between the 
roasting* of lumps and fines is the time requisite for their oxida¬ 
tion. Oxidation is almost instantaneous for an infinitely small 
particle of any sulphide, and the time increases with the cubic 
contents of the fragment, until such a size is reached that the air 
fails to penetrate the thick crust of oxides formed upon the out¬ 
side of the lump of ore or matte, and all action ceases. 

It might seem, therefore, that the process of pulverization 
should be pushed to extreme limits, and that the best results 
would be obtained from the most finely ground ore. But this is 
by no means the case in actual practice; for other conditions 
arise that more than counteract any advantage in time. The 
chief of these, aside from the difficulty and expense involved in 
the production of such fine pulp, are the losses in metal, both 
mechanical and chemical, that occur with every movement of the 
ore, and reach an enormous aggregate before the operation is 
completed; and the liability to fritting or sticking together in the 
calcining-furnace, regardless of the greatest possible care in this 
process. The oxidation of the particles takes place with such 
rapidity that a temperature is generated above the fusion-point 
of ordinary sulphides. 

Still further objections could be mentioned; but those already 
adduced are sufficient to limit the degree of pulverization for the 
principal portion of the ore, although a greater or less propor¬ 
tion, according to the machinery used for the purpose, is crushed 
to an impalpable dust, and causes a considerable mechanical loss, 
in spite of all provision for its prevention. 

The best size to which to crush varies with each individual 
ore, and is entirely a matter of trial and experience; nor should 
any one responsible for the calcination of any given material rest 
satisfied until he has determined by actual and long-continued 
experiment that the substitution of either a coarser or a finer 


124 MODERN AMERICAN METHODS OF COFFER SMELTING. 

screen for the size in use will he followed by less favorable re¬ 
sults. 

This may be arrived at by careful comparative determinations 
of the residual sulphur contents after the calcination of material 
crushed through screens of various sized mesh and roasted for 
the same length of time, careful consideration also being given 
to the cost of crushing in each case, to the condition of the ox¬ 
ides of iron present (the sesquioxide is an unfavorable constitu¬ 
ent in reverberatory smelting), and, above all, to the quantity of 
flue-dust formed, and loss of metal by volatilization. 

It is evident that such diverse and obscure questions can only 
be accurately determined by extensive and long-continued trials. 
But the result is well worth the labor, and in these days of almost 
universal information and close competition, it is only by such 
means that any decided advantage can be obtained. 

While mattes, speiss, or similar products of fusion must always 
be granulated or pulverized to the degree required for calcina¬ 
tion, it is not an uncommon quality of sulphide ores either to 
decrepitate, or else to fall to pieces when heated, by the mere 
moving from place to place in the furnace, to such an extent that 
the charge may be made up of pieces from the size of a walnut 
down, without affecting either the time requisite for the oxida¬ 
tion or for its perfection. The product will be an almost homo¬ 
geneous and impalpable powder. 

A more striking illustration of such a condition of affairs can 
hardly be found than in the case of the concentrates from the 
Parrot Company’s mine at Butte, Montana. 

In this instance, the process of subdivision resulted from two 
different causes. The iron pyrites that forms the larger portion 
of the ore decrepitates into very minute cubes, which are subse¬ 
quently reduced to a fine powder by oxidation, while the frag¬ 
ments of pure copper ore—bornite—seem gradually to diminish 
in size by the wearing away of the surface as it becomes earthy 
and friable from the superficial formation of oxides. 

This latter phenomenon may also be observed to a less extent 
in the calcination of mattes when they are of a sufficiently soft 
or porous nature; but in roasting a considerable quantity of a 
very low-grade matte (from 10 to 15 per cent, of copper) that 
had been obtained in hard polished granules by tapping into 
Avater, it was found impossible materially to alter either the size 


125 


CALCINATION OF ORE AND MATTE. 

or shape of the grains, many of which were as large as an army 
bean, or satisfactorily to reduce the percentage of sulphur, even 
by long exposure to a temperature closely approaching its fusion- 
point. 

On the other hand, quite satisfactory results are obtained in 
the case of richer matte (from 30 to 40 per cent, of copper) by 
granulation in water; and, in many of the foreign works, this is 
the only means provided for the preparation of the matte for the 
process of roasting; but it must lie remembered that this practice 
is confined to the English reverberatory method, where it is not 
desired to remove more than 50 per cent, of the sulphur by roast¬ 
ing, and where a portion of sulphides still remains in the calcined 
matte that would be entirely unsuited to the so-called “ blast¬ 
furnace ” method of matte concentration in cupolas, as usually 
practiced in this country. 

Although the results described, as obtained by granulation, 
may lie improved upon by careful attention to the temperature 
and pitch of the matte when tapped, and especially by care and 
experience on the part of the smelter, this practice cannot be 
recommended, excepting under peculiar conditions and in remote 
situations, where improved crushing machinery is not obtainable, 
or where the physical condition of the matte is particularly favor¬ 
able to the production of porous and friable granules. Nor is 
anything gained by its employment for the purpose of avoiding 
the preparatory breaker, and obtaining at once a material suffi¬ 
ciently subdivided for immediate treatment in the final pulveriz¬ 
ing apparatus; for, although, in this practice, the larger granules 
are broken and crushed into a condition favorable for the calcin¬ 
ing process, a large proportion of the entire mass is already so 
minute as to pass through the crushing apparatus untouched in 
the shape of minute spherical pellets or globules, which present 
the least possible surface to oxidation, and retain a hard, glossy 
'surface. These grains are scarcely affected by any moderate 
temperature, and may even undergo complete fusion without any 
perceptible loss of sulphur. Not many years ago, the question 
of economy might have influenced the adoption of this practice; 
but at the present time, and in view of the improved and com¬ 
paratively inexpensive machinery at our disposal, it is probable 
that the inconvenience, danger, and other drawbacks inseparable 
from the projection of large quantities of molten sulphides into 


126 MODERN AMERICAN METHODS OF COPPER SMELTING. 


water, and their subsequent recovery from the reservoir or what¬ 
ever vessel is employed for the purpose, more than outweigh the 
cost of crushing by machinery. 

It is impossible to lay down fixed rules for the degree of pul¬ 
verization of any material best suited to roasting. Each case 
must be decided according to its own peculiar conditions, includ¬ 
ing the cost of labor and power, and the capacity and quality of 
the mechanical means available. 

Bearing in mind the results that may, in certain exceptional 
cases, come from decrepitation, it may be assumed that a reduc¬ 
tion in size beyond one-twelfth of an inch is seldom advanta- 
geous in treating ores, and that the presence of a large proportion 
of sulphides or of a particularly porous or friable gangue may 
permit an increase of the screen mesh to one-eighth inch or more. 
With mattes, a slightly finer standard (from one-twelfth to one- 
sixteenth inch) may be employed. 

The proportion of the ore reduced to a minuteness neither 
intended nor desired depends materially upon the means em¬ 
ployed for crushing j and as the mechanical loss and other evils 
enumerated increase in direct ratio to the amount of fine dust in 
the charge, it is evident that, other things being equal, the ap¬ 
paratus best adapted to the breaking of ore or matte is that 
which produces the smallest proportion of fines. 

CRUSHING MACHINERY. 

The crushing machinery used for the purpose under discus¬ 
sion may be divided into two classes 

1. For preparatory crushing: Jaw-breakers of various pat¬ 
terns. 

2. For final pulverization: Stamps, Ball pulverizers, Chib 
mills, various patent pulverizers and grinders, Cornish rolls. 

I. MACHINES FOR PREPARATORY CRUSHING. 

The jaw-crushers in almost universal use are eminently satis¬ 
factory as regards economy, capacity, and general suitability to 
the purpose for which they are intended. A few deductions from 
long-continued trials of almost every well-known pattern of 
breaker may be useful. Ordinary prudence will suggest to the 
inexperienced the choice of some form of machine long and favor¬ 
ably known to the public, and nothing can be more foolish than 


CALCINATION OF ORE AND MATTE. 


127 


tlie selection of some novel and much vaunted but untried ap¬ 
paratus. 

A machine should lie selected that has stood the test of years, 
and is manufactured by some well-known and reputable firm. 
Liglit-built machines should lie particularly avoided, as the strain 
exerted upon certain parts of every breaker, especially when 
clogged with clayey ore and set to crush fine without shortening 
the stroke of the jaw, is something enormous, and only to be 
successfully encountered by superabundant strength in every 
portion of the apparatus. This is well exemplified in the break¬ 
ers turned out from the foundries of those manufacturers who 
have long made a study of this particular business, and who 
have gradually added an inch of metal here and a half inch 
there, as time and trials have developed the v r eak points of the 
machine, until it may appear bulky and clumsy beside the light 
and elegant models of some of their later competitors. Unless 
ore is delivered to the smelter in unusually large lumps, the 7 by 
10-inch jaw-breaker will be found most convenient for general 
work, and not so heavy as to demand special arrangements for 
its setting-up. (These, figures refer to the size of the opening be¬ 
tween jaws—the smaller number indicating the distance between 
the fixed and movable jaw, while the larger gives the measure¬ 
ment at right angles to this.) Such a machine can be set to 
break to a maximum diameter of three-quarters of an inch, and 
has a capacity equal to any ordinary demands, although varying 
greatly with the size of the discharge opening and quality of 
the material crushed. The setting-up and management of this 
machine are matters of too universal knowledge to require 
further attention; but it may not be generally understood that 
the substitution of smooth jaw-plates for the corrugated ones 
usually employed will greatly increase the proportion of fines in 
the product. 

As the ore usually passes directly from the breaker to the 
rolls—better with the interpolation of a short screen to remove 
such as is already sufficiently fine; and as in fine crushing the 
capacity of the breaker, even when set up to its closest prac¬ 
ticable limits, usually greatly exceeds that of the rolls, a decided 
increase in the work performed can be most economically and 
easily effected by introducing a second fine breaker between the 
coarse crusher and the final pulverizer. This machine may be of 


128 MODERN AMERICAN METHODS OF COPPER SMELTING. 


quite light construction, should have a very long, narrow jaw 
opening—say 2 by 12 inches—a slight u throw,” and move at a 
high speed. 

It is in this direction that the most important improvements 
in fine crushing machinery may be looked for, and it is probable 
that the crushing and, still more important, the discharge area 
may be most advantageously increased by the employment of a 
multiple-jawed machine. This apparatus—when used merely as 
an intermediate crusher—will reduce the product of the coarse 
breaker to the size of corn, or even smaller, thus greatly lighten¬ 
ing the work of the finishing pulverizer. 


II. MACHINES FOR FINAL PULVERIZATION. 

The apparatus at all suited for this purpose may be brought 
under the following heads: 

Stamps. Miscellaneous patent pulverizers. 

Ball pulverizers. Multiple jaw-crushers. 

Chilian mills. Cornish rolls. 

Stamps, although universally known and always reliable, pro¬ 
duce far too great a proportion of fine dust, besides being un¬ 
necessarily expensive, both as regards first cost and subsequent 
running. 

The Ball pulverizer, when properly constructed, has the merit 
of compactness, slight cost, economy in running, and several 
other advantages, but is of insufficient capacity, and, like stamps, 
is better calculated for the production of fine pulp than of the 
material required for calcination. 

Chilian mills have obtained a strong foothold in England for 
certain metallurgical purposes, but are expensive and cumber¬ 
some, have a very small capacity, and are peculiarly adapted to 
the production of impalpable dust. 

The miscellaneous patent pulverizers now offered for sale would 
require a considerable space for their enumeration. In many 
cases, they possess much merit; but although differing to an ex¬ 
treme in almost every other particular, are pretty well united in 
producing a pulp containing too much dust in proportion to the 
granules. 

Multiple jaw-crushers have already been referred to as promis¬ 
ing much for the future. This construction admits of an 


CALCINATION OF ORE AND MATTE. 


129 


enormous area of discharge opening, and since the breaking of 
each fragment of rock is accomplished by the approach of two 
opposing surfaces, which yet can never meet, all particles suffi¬ 
ciently fine are at once removed. There is reason to hope and 
expect that these machines will soon be perfected j in which case, 
nothing yet invented could be better suited to the production of 
just such material as is demanded both for concentration and for 
the variety of calcination now under discussion. 

Cornish rolls .—No other class of machines can compare with 
the Cornish roll for capacity, economy, and certainty in crushing 
every variety of ore and matte for the purpose just indicated. 
But inasmuch as the various patterns of this machine differ 
almost as much among themselves in efficiency and capacity as 
they do from the other pulverizers already mentioned, and as an 
examination of a large proportion of the roller plants in actual 
use at the present time in this country indicates a great want of 
care in both construction and management, and tendency to be 
satisfied with a considerably lower standard of excellence than 
might easily be attained, it seems desirable to draw attention to 
such points as seem to particularly demand supervision or refor¬ 
mation. 

Rolls should be ordered onlv from the best makers, who can 
refer to numerous similar machines of their manufacture in long 
and successful operation, nor should the metallurgical engineer 
forget that much of the work for which rolls are made, and in 
the performance of which they give perfectly satisfactory results, 
is for phosphates, gypsum, lead ore, or similar soft or brittle sub¬ 
stances, whose crushing bears no relation to that of the low-grade 
matte and tough quartzose—or hard pyritic—ores that are gen¬ 
erally the object of calcination. Certain low-grades of matte, 
especially when produced in blast-furnaces, contain a large pro¬ 
portion of various indefinite compounds of copper, iron, and 
sulphur that are almost malleable, and would inevitably destroy 
any of the ordinary light-weight, low-priced rolls so frequently 
considered sufficient for general purposes, and occasionally placed 
in metallurgical establishments with mistaken notions of econ¬ 
omy. 

The most important proportions, to be noticed in the type of 
rolls required for the purpose under discussion, are great diam¬ 
eter of the body of the roll in proportion to its face—or, 


130 MODERN AMERICAN METHODS OF COPPER SMELTING. 


better, 3 to 1; great strength of axle, which may be with advan¬ 
tage one-quarter of the total diameter of the roll, including shell; 
great length and rigidity of bearings, which may be of Babbitt- 
metal, or, still better, of brass; proper size and weight of fly¬ 
wheels, and a general strengthening and reinforcement of all 
parts of the machine that are found weak or doubtful on com¬ 
parison with the increased capacity of the portions just named. 
The frame in particular will require a decided augmentation of 
strength to correspond with the additions enumerated, and may 
advantageously be cast in separate halves, to avoid the incon¬ 
veniences arising from its bulk and weight. The best material 
for the roll-shell, as well as the most convenient means for hold¬ 
ing the two massive rolls in apposition, while provision is yet 
made for the passage of any infrangible or incompressible sub¬ 
stance, are questions that have drawn out a variety of opinion 
and practice. 

Two varieties of shell only demand consideration for the 

«/ 

crushing of hard ores and mattes. 

1st. White iron, chilled to the depth of nearly an inch, and 
so evenly that no variation in wear is detected on the surface 
after the passage of a thousand tons or more of the hardest 
material. 

2d. Soft steel, such as is produced by the Siemens-Martin 

method at a very moderate cost. 

*/ 

Such chills as are here indicated, and as are alone satisfactory 
in practical work, can only be obtained by careful manufacture, 
and the ordinary chilled shells advertised as perfectly satisfactory 
by the greater number of manufacturers are comparatively worth¬ 
less, and a source of constant annoyance and expense. A pair 
of chilled shells of 36-inch diameter, Id-inch face, crushed approx¬ 
imately 22,000 tons of medium ore, taking it from the fine 
breaker, 1 d inches, and reducing it to about five-eighths of an 
inch in size before being worn out, the chilled surface wearing 
smoothly and regularly away to the depth of over half an inch 
before any notable irregularities appeared. 

It is always advantageous to have all the rolls in use in any 
establishment of the same diameter and make, as in this wav a 
very great saving is effected by using all new shells for fine 
crushing, and when too much worn to yield economical results 
in this situation, to pass them on to the coarse crushing rolls, 


CALCINATION OF ORE AND MATTE. 


131 


where they may perhaps serve an equally long time before being 
finally discarded. 

It is by no means generally known that the hardest chilled 
iron may be turned with an ordinary tool without difficulty if a 
sufficiently slow motion is made use of in the process.* In this 
way, a set of shells may be preserved in condition for fine crush¬ 
ing for a much longer period than is usual, as the shells are 
almost invariably incapacitated for this purpose by their tendency 
to wear hollow in the center. This fault may be partially ob¬ 
viated by a simple device by which the stream of ore as fed to 
the rolls is diverted from the center and directed to the lateral 
portions of the roller surfaces; but is much more immediately 
and effectually remedied by turning the surface smooth under 
the precautions just indicated. 

Steel shells also give excellent satisfaction, and are quite easily 
turned, as onlv soft steel is used in their manufacture. 

No one who has watched the constant jumping of all ordinary 
rolls, with the accompanying separation of the opposing surfaces, 
and has noted the inevitable escape of a pound or more of coarse 
material through the crevice thus formed, can doubt the increase 
in capacity that would arise from the rigid fixation of the crush¬ 
ing surfaces at such a distance from each other that nothing 
could pass between them without being reduced to the desired 
size. Any proposition to this effect is usually met with the ob¬ 
jection that the rolls would frequently become u stalled ” for want 
of power, or else that constant breakages would arise from the 
passage of a bit of steel or some similar infrangible substance. 
The first objection is too trivial to require notice, while the sec¬ 
ond may be met in various ways: By either increasing the 
strength of the springs by which the rolls are maintained in ap¬ 
position, to such an extent that no substance capable of being 
crushed without detriment to the machine can pass them without 
being crushed; or by abolishing springs entirely, and providing 
some weak point in the apparatus that shall break before the 
strain becomes dangerous to other and more expensive parts. 

Both of these methods are in satisfactory use, the latter, how- 

* The author desires to acknowledge his indebtedness to Mr. Franklin 
Farrel, of Ansonia, Conn., for this important point in the manipulation of 
chilled iron, as well as for many novel and useful suggestions in connection 
with rolls and crushing machines. 




132 MODERN AMERICAN METHODS OF COPPER SMELTING. 


ever, being' suited only to tine crushing; the employment of a thin 
cast-iron breaking-cup renders its application simple and econom¬ 
ical ; while the former improvement is best effected by the use of 
strong duplex steel car-springs, or heavy rubber springs, which 
are in use at many places, giving almost universal satisfaction. 

In erecting a new roller plant, provision should be made for 
convenience in changing the shells, which is a heavy and tedious 
task unless ample space is reserved overhead for the employment 
of block and tackle. A gain of several hours will be effected by 
having in readiness a duplicate set of roller-shafts as well as shells, 
so that each old roll may be lifted entire from its bearings, and 
its new substitute lowered at once into the vacant place. 

Rolls frequently fail to meet expectations from being run at 
too low a speed. Seventy-five or even one hundred revolutions 
a minute for a 3G-inch roll of the most modern construction is not 
too great, and can be used with no untoward results beyond the 
increased production of fine dust from the violent impact of two 
solid bodies moving at such a high velocity. Forty to fifty revo¬ 
lutions is enough for geared rolls. 

Unless rolls are specially constructed for the purpose, nothing 
is gained in setting them so that their surfaces are in direct con¬ 
tact, even for the finest crushing, as they will constantly choke 
and give trouble, without yielding nearly as large an amount of 
product of the desired fineness as when they are set slightly apart, 
and the product that is not fine enough to pass the screen is re¬ 
turned to them. 

Nearly all of the difficulties and annoyances experienced with 
elevators may be avoided by constructing them with a capacity 
greatly beyond their apparent requirements. 

Strong, large cups should be selected, never less than ten 
inches in width, except for handling very fine material, and traw 
eling at a rate of at least 280 feet a minute. These should be 
strongly riveted to a four-ply rubber belt, except in cases of per¬ 
fect freedom from moisture, where leather is preferable. 

Double chain elevators running over sprocket-wheels also do 
excellent work when properly made. 

The feeding and management of the crushing plant should be 
intrusted to a careful and experienced man, any infraction of this 
rule being almost certainly followed by annoyance and loss. 

Its capacity varies greatly with the quality of the material and 


i 


CALCINATION OF ORE AND MATTE. 


133 


the fineness to which it is crushed, diminishing very rapidly with 
the degree of comminution. 

As a rough indication of what may be expected from the 
variety of plant just indicated, consisting of a 7 by 10-inch 
breaker, and a single pair of 36-inch rolls, with screen and ele¬ 
vator, the following figures are given from the author’s note¬ 
book : A hard but brittle siliceous ore, carrying a small percent¬ 
age of pyrites, was crushed through an 8-mesli screen at the rate 
of 2,236 pounds an hour. The substitution of a 12-mesh screen 
reduced the hourly production to 1,560 pounds. 

A hard and tough matte was crushed through the latter screen 
at the rate of only 960 pounds an hour, nor can a much greater 
duty than the above lie expected from any similar plant. 

Any estimate of machinery and of such portions of the gen¬ 
eral plant as can be purchased ready for use, and consequently 
possess a specific market value, public to all, does not come within 
the scope of this treatise. Rolls are now made without gears, 
each roll being run by an independent belt. They give great 
satisfaction. 

CALCINING FURNACES. 

The furnaces suited especially to the oxidizing-roasting of 
sulphureted ores and mattes in a pulverized condition may be 
included under the following heads: 

I. Shaft-furnaces. 

II. Revolving cylinders. 

III. Automatic reverberatory furnaces. 

«/ 

a. With stationary hearth. 

l). With revolving hearth. 

IV. Ordinary reverberatory furnaces. 

a. Open-hearth furnaces. 

b. Muffle furnaces. 

I. SHAFT-FURNACES. 

This group includes some of the most important and useful 
appliances for the roasting of sulphureted substances, where the 
utilization of the fumes for the manufacture of sulphuric acid 
forms a part of the process of calcination. 

If the question of acid manufacture be left entirely out of 
consideration, and the comparative economy of each method of 
calcination be judged solely upon its own merits, it is doubtful 


134 MODERN AMERICAN METHODS OF COPPER SMELTING. 


whether resort would he had to these furnaces, save under excep¬ 
tional conditions, as their limited capacity, great cost of con¬ 
struction, and imperfect work, except under the most skillful 
management, would effectually bar their introduction. But 
under the stimulus arising from the enforced manufacture of 
acid from pulverized pyrites, and the consequent necessity of em¬ 
ploying some form of automatic furnace in which the gases aris¬ 
ing from the oxidation of the ore are kept separate from the prod¬ 
ucts of combustion of the fuel, this type of calciner has received 
such attention and study that it promises fairly to rival the most 
economical form of roasting apparatus known to metallurgy. 
The student is referred to Lunge’s work on the manufacture of 
sulphuric acid for full details regarding this and other forms of 
furnace suited to the calcination of ores in connection with acid¬ 
making. 

The Gerstenhofer shelf-furnace was the first successful cal¬ 
ciner* of this type, and is still largely used, though becoming 
gradually supplanted by improved modifications. The few fur¬ 
naces of this pattern that have been constructed in the United 
States have failed to answer the desired purpose, owing to im¬ 
perfect construction, poor refractory materials, and want of skill 
in management. The Gerstenhofer furnace consists of a vertical 
shaft, surmounted by a mechanical device for feeding the pulver¬ 
ized sulphides in any desired quantity, and containing a great 
number of parallel clay ledges of a triangular form, one of the 
flat surfaces being placed uppermost. These are so arranged as 
to obstruct the ore in its passage, and delay it sufficiently to 
effect a certain degree of oxidation, which is seldom perfect 
enough to yield the desired result without a supplementary cal¬ 
cination in some other form of furnace. The front wall of the 
shaft is pierced by parallel rows of rectangular openings, for 

*As this treatise is intended to deal exclusively with American methods 
and practices, any detailed description of various valuable automatic cal- 
ciners that in other countries have proved highly successful is omitted. 
Nor will consistency permit the elaborate description of certain American 
inventions—such as the Stetefeldt and Howell roasting furnaces—which, 
although invaluable for the chloridizing-roasting of silver ores, or even for 
the thorough calcination of fine pyrites for chlorination, have not yet been 
adopted to any considerable extent by the copper smelter. This is of the 
less consequence, as full descriptions of all these various forms of apparatus 
are accessible to the public. 



CALCINATION OF ORE AND MATTE. 


135 


the purpose of changing the clay shelves or of cleansing the 
same. 

The oxidation of the sulphides generates sufficient heat for 
the proper working of the process, so that the sulphurous gases 
may he obtained for the manufacture of acid free from any prod¬ 
ucts of the combustion of fuel. 

The Stetefeldt furnace, so invaluable for the chloridizing- 
roasting of silver ores, is a shaft provided with a grate for the 
generation of such a degree of temperature as would be lacking 
in the roasting of ores so poor in sulphur as those usually ex¬ 
posed to this treatment, as. well as an auxiliary fire-place for the 
more perfect chloridizing of the flue-dust, which, owing to the 
fine pulveriztaion of the ore and the strong draught essential to 
the proper working of the apparatus, is formed in unprecedented 
amounts, and pretty thoroughly regained in ample dust- 
chambers. 

The employment of an auxiliary fire-place, and the invention 
of a highly ingenious and perfect automatic ore-feeder, constitute 
important claims to originality that are frequently overlooked by 
writers in commenting on this furnace. Its capacity is very 
great, 60 tons in twenty-four hours being easily worked in one 
of the large-sized furnaces of this type; and were it possible to 
obtain equally good results by employing it for oxidizing- 
roasting, it would be the most valuable addition to the modern 
metallurgy of copper. But as it is at the present time, it cannot 
be enumerated among the resources of the copper smelter, 
although late experiments indicate the probability of its success¬ 
ful adaptation to this purpose. 

The English acid-makers have introduced various modifica¬ 
tions of the two last-named furnaces for the desulphurization of 
cupriferous iron pyrites. These may be found in Lunge’s work, 
and are said to possess considerable capacity and yield excellent 
results. 

II. REVOLVING CYLINDERS. 

These also are extensively and advantageously used for the 
chloridizing of silver ores, having a considerable capacity, and 
effecting a thorough chloridization at a very moderate cost. 
They consist essentially of a horizontal or inclined brick-lined 
iron cylinder, revolved slowly bv gearing, and having a fire-place 
at one end—or at both ends, used alternately. 


136 MODERN AMERICAN METHODS OF COPPER SMELTING. 

Numerous experiments as to their applicability to the oxidiz- 
ing-roasting of pyritous ores have been carefully carried out, 
and, while the author has not found it economical for this pur¬ 
pose in its original form, late experiments have shown its perfect 
adaptation to this class of work. 

A still further advance has been made by Mr. James Douglas, 
who, by introducing an interior central flue for the passage of 
flame and smoke, and carefully graduating the supply of air, has 
combined the advantages of the revolving cylinder and the muffle 
furnace. 

Since publishing the first edition of this book, great advances 
have been made in calcining ores in powder form, in automatic 
furnaces. 

Both the O’Hara plow furnace and the shelf furnaces for 
acid-making have their advocates 5 but there is little doubt that, 
at the present time, the modified and improved Bruckner’s cyl¬ 
inder stands pre-eminent as the most satisfactory and econom¬ 
ical of all automatic calcining furnaces for pulverized ore. 

In describing this furnace, it would be unjust not to mention 
Messrs. Fraser and Chalmers, of Chicago, whose energy in intro¬ 
ducing it, and in going to great trouble to modify and improve 
it, and adapt it to the desulphurization of copper ores and con¬ 
centrates, has earned the gratitude of all copper-smelters. To 
Mr. W. R. Eckart, the profession is indebted for the detailed 
drawings of the cylinders now giving such satisfaction at the 
Anaconda Works, in Montana. 

Through the courtesy of friends I am enabled to now give 
absolutely reliable information concerning the results of the en¬ 
larged and improved Bruckner’s cylinders now in use, having 
detailed information from every works in Butte City where they 
have been introduced. 

The large cylinders, as now made, are 8 feet 6 inches in 
diameter by 18 feet 6 inches long. 

They are lined with one thickness of good red brick, though 
doubtless, where fire-brick are cheap, it will pay to use them, as 
they withstand the mechanical wear and tear much longer than 
red brick ; owing to the care bestowed upon then* manufacture, 
they are much more regular in shape, thus forming a tighter and 
more perfect circle inside the iron shell, the strength of which 
can be still more increased by having the brick molded to order 




























































































































































































































































































































































































































































138 MODERN AMERICAN METHODS OF COPPER SMELTING. 

to suit the inner circle of the cylinder. Again, they are much 
more durable when exposed to dampness than are red brick, 
which are quickly destroyed if dripping concentrates are fed into 
the red-hot furnace. 

But even wdiere red brick are used, the lining lasts about 18 
months when properly put in, and as this is the principal cost of 
repairs during the first few years, it is evident that it must be 
very small. 

As will be seen in the accompanying perspective sketch of the 
furnace, it has a double-snouted feed-hopper, with two feeding- 
holes, and two others opposite them, half-way around the cir« 
cumference of the shell, so that it can be discharged without 
much loss of time. It is best, of course, where possible, to dis¬ 
charge the roasted ore directly into the reverberatory smelting 
furnaces, if such are used, or into an adjacent vault, where the 
heat will not be rapidly dissipated. But in works where the cal¬ 
cined ore must be first cooled down before going to the smelter, 
the cooling arrangements must be of large capacity to handle 
the heavy charge of ore employed. 

In the improved cylinders, the fire-box is really a car, running 
on a track at right angles to the longitudinal direction of the 
cylinders, and having a short flue in one side that comes exactly 
opposite the throat of the furnace. In this way, the fire-box can 
be run opposite a cylinder, which contains a fresh charge, and 
fired on until the sulphur is fairly kindled. Then the movable 
fire-box may be wheeled along to a neighboring cylinder, and the 
first one left to complete the combustion of the sulphur with 
free access of air, and undisturbed by the reducing gases that 
pass through an ordinary grate. After the combustion of the 
sulphur, it is necessary for a perfect roast to again connect the 
fire-box with the cylinder and supply a little extraneous heat to 
complete the decomposition of the sulphates. 

It is estimated that two horse power are required to drive a 
charge cylinder at average speed. The size and weight of the 
ore-charge varies greatly with its quality, percentage of sulphur, 
specific gravity, etc. 

At the Anaconda Smelting Works, one hundred and fifty six 
[156] of these cylinders are constantly in operation, engaged 
principally in desulphurizing concentrates containing about 35 
per cent, of sulphur. Here the charge is 18,000 pounds of con- 


CALCINATION OF ORE AND MATTE. 


139 


centrates, which in 24 hours are roasted down to 10 per cent, of 
sulphur. It has been found by experience that, in 36 hours, the 
sulphur is reduced to 3 per cent., which would be far too low for 
the subsequent smelting operation. 

This must certainly be the largest automatic calcining plant 
in the world, as some 1,500 tons of ore are roasted every 24 
hours. 

It takes 2,000 pounds daily of Rock Springs coal to fire each 
cylinder. This is very inferior in quality to Eastern coal, and it 
would be safe to estimate that 1,500 pounds of Pennsylvania coal 
would be sufficient for 9 tons of ore. 

As two men per 24 hours will attend three furnaces, it is evi¬ 
dent that the cost of calcination is reduced to a lower figure by 
the use of these cylinders than has ever hitherto been reached. 

Other smelting works in Butte, Montana, report almost iden¬ 
tically similar results from the use of these cyfinders, Mr. W. A. 
Clarke reporting that he is roasting a charge of 24,000 pounds 
down to 12 per cent, of sulphur in 30 hours, the ore consisting 
of three-fourths concentrates, carrying 40 per cent, sulphur, and 
one-fourth screenings containing 25 per cent, zinc-blende and 50 
per cent, silica, using one cord of pine wood every 8 hours. 

The loss of silver [as most of the Butte copper ores carry a 
paying quantity of silver] is not apparent, and if sufficiently ex¬ 
tensive dust-chambers are provided, there is very little lost in 
flue-dust. 

The capacity of any form of calcining furnace, running on 
pulverized material, depends upon its draught. The more cubic 
feet of am you can pass through the furnace per minute, the more 
rapidly will the process of oxidation proceed. Of course there 
must be a limit beyond which any excess of air will only be a 
detriment, but I have never yet reached that point in my own 
practice, nor seen it reached. 

I agree entirely with Mr. R. P. Rothwell, who, having had 
much experience in the roasting of auriferous, arsenical pyrites 
in cylinders, suggests the employment of a fan to produce a 
proper and measured draught. He also insists on the importance 
of making the first dust-chamber in the series (the one next to 
the furnaces) very large and easy of access, by which plan almost 
all of the dust will settle in it, and can be easily removed with¬ 
out interfering with the more distant ones for many months. 


140 MODERN AMERICAN METHODS OF COPPER SMELTING. 

. I 

The size of the grains of ore to he roasted has a most impor¬ 
tant effect upon the rapidity and perfection of the process. Of 
course no sensible person would use chunks of ore the size of a 
hen’s egg (as I have more than once seen tried by inexperienced 
persons), as they not only tend to rapidly destroy the brick lining 
of the cylinder, but also retard the process of oxidation almost 
indefinitely. 

The only exception to this rule is in the case of certain ores 
containing much iron-pyrites or zinc-blende, intergrown with the 
particles of rock in such a manner that they begin to decrepitate 
before a red heat is reached, and soon fly into a granular powder 
as completely as though they had passed through a proper 
crusher, and with the formation of much less dust. 

I need hardly say that, in erecting a cylinder, or indeed any 
machinery, great attention should be paid to the foundations, 
which should have a solid base, with the rock or brick-work laid 
in thorougldy good cement mortar, and allowed to set before the 
timbers are placed upon it. These should be framed with the 
greatest care, long bolts passing down through channels in the 
masonry, provided with a heavy washer below, and arranged so 
that a long wrench can be introduced to hold the bottom nut. 
If the bearings are not absolutely true and level and in line at 
the start, and placed so that they will remain so, or can at least 
be easily lined-up, there will be endless trouble and wear on the 
running parts of the cylinder, besides a great waste of power,, 
amounting, in certain instances that I have seen, to an increase 
of 100 per cent, or more in the fuel used to drive it. 

These cylinders are usually arranged with fast and slow speed, 
so that, without altering the speed of the engine, the cylinder 
may be revolved slowly during the roasting period, and more 
rapidly whilst the ore is discharged. 

A clutch of a peculiar construction is provided, so that they 
can be thrown in and out of gear with little effort, and with no 
undue jerking, or strain on the gear wheels. 

By a careful comparison of the results furnished me by those 1 
who use these cylinders with the large reverberatory calciners,. 
described at length in this book, I find that, under the conditions 
of high wages and expensive fuel obtaining at Butte City, Mon¬ 
tana, the saving in cost by using the calciners instead of the. 
reverberatories is about 40 per cent. 


CALCINATION OF ORE AND MATTE. 


141 


Where wages are low, this saving would he greatly reduced, 
and under some conditions that prevail in the United States, I 
think that, on the whole, the ordinary calciner might he equally 
economical. But there can he no douht of the economy of this 
cylinder in the mining regions of the West. 

By the courtesy of the Chicago Iron Works, I am enabled to 
present some excellent drawings, showing the details of the 
Bruckner cylinders manufactured hy them, and which are doing 
very satisfactory work in Montana and elsewhere. 

Direct statements from those who are using them show that 
my estimate of a saving of 40 per cent, of the costs of calcining 
hy using these large cylinders in lieu of even the most modern 
hand-calcining furnaces, is hy no means excessive, and in some 
instances does not represent the full amount saved. 

III. AUTOMATIC HEARTH FURNACES. 

a. With stationary hearth .—This subdivision is best repre¬ 
sented by O’Hara’s mechanical furnace, which differs only from 
an ordinary reverberatory calciner hy being provided with an 
automatic stirring apparatus. This consists of two or more end¬ 
less chains, to which are fastened at regular intervals plow-shaped 
scrapers, which traverse the long, narrow hearth longitudinally, 
thus stirring the ore and constantly presenting fresh surfaces to 
the action of the air. It is looked upon with favor in Butte 
City, and is preferred hy the Butte & Boston Copper Co. to all 
others. 

The Spence automatic desulphurize!* is a promising member 
of the same division, and is in successful operation at some of 
the acid-works near New York where copper-bearing iron pyrites 
are used. 

The space occupied by a Spence furnace is about 34 feet by 
18 feet. When two double furnaces are coupled together and 
run by one engine (as preferred in all cases), the space required 
is 34 feet by 32 feet. A building 40 feet by 40 feet is therefore 
necessary to accommodate this plant with a shed-roof, if connec¬ 
tion is made to towers and chambers, or an ordinary flat-roof 
building with supporting posts placed between the furnaces, 
when connected directly with the chimney, as in the process of 
desulphurizing gold ores. 

There are several practical points of excellence about the fur- 


142 MODERN AMERICAN METHODS OF COPPER SMELTING. 

nace that entitle it to careful examination by engineers. The 
action of the furnace will be understood to be automatic, the ores 
being elevated from the furnace-floor, brought in from the floor 
above, or by other means supplied in quantities as required to 
keep the hoppers full. This matter of detail will readily be un¬ 
derstood by those practiced in the handling of ores from different 
levels, and the drying of the ores (if wet) will also be understood 
to be a simple matter when small quantities are regularly fed. 

The movement of the rack (with rakes inside the furnace) 
opens the ports for the admission of fresh ore from the hoppers 
to the first shelf, and the discharge of finished or calcined ore 
from the lower shelf into cars. When the rakes have finished 
the forward stroke, the engines reverse automatically, and the 
rack returns to, and stops in, position. 

This automatic and regular method of feed and treatment of 
the ore on the bed of the furnace is the result of years of study 
and practice, directed to the object of replacing by a uniform me¬ 
chanical procedure the discretionary operation of hand labor. 

By study of the plant now in operation, the following conclu¬ 
sions are reached: 

1. The constituent elements of the ores being first determined, 
the feed and discharge are regulated to exact amounts in pounds, 
and the number of charges fed into the furnace is duly regis¬ 
tered. 

2. The auxiliary engine being set to start the motive power, 
say every five minutes, and the time required for the forward 
and back stroke being, say, one and a half minutes, it follows 
that the interior parts of the rakes are exposed to action of heat 
and acid fumes but one-third of the time, thus approximating 
manual labor in wear and tear of plant. 

3. The draught of air being regulated and controlled by the 
chemist at will, insuring the proper oxidation of the ores, and no 
more, less chamber space must be required than by any other 
process of burning pyrites, and, moreover, no special care need 
be given to location of plant, since strong winds or variable cur¬ 
rents can have no effect in causing “ blow-outs ” of gas at the 
doors. 

4. The movement of the ores from the hoppers to the dis¬ 
charge-opening is accomplished by a system of reversed teeth, 
which are positive in action. 



--- r 


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IMPROVED BRUECKNER’S CYLINDER, AS USED FOR ROASTING COPPER ORES. 

Side Elevation. 


Front Elevation. 
(Fire-box removed.) 

































































































































































































































































































































































































































































































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CALCINATION OF ORE AND MATTE. 


143 


The deterioration or destruction of cast-iron rakes and teeth 
has been reduced to a minimum by the simple but novel idea of 
burying the parts in ore, which accumulates at the front of the 
furnace-beds when the rakes are at the position of rest. 

5. Pyrites “ smalls/’ such as are found in Virginia, and at the 
Milan and Capelton mines, carrying 47, 45, and 40 per cent, of 
sulphur respectively, can be calcined with two double Spence 
furnaces, run by one engine at the rate of from 15,000 to 20,000 
pounds per day of twenty-four hours, the cinders containing 
from 1.1 to 21 per cent, of sulphur. 

It is claimed that larger amounts of u smalls ” containing cop¬ 
per, blende, etc., can be put through, and double the above quan¬ 
tity, where sulphur fumes are passed directly into the air—as 
would be the case in working auriferous concentrates. 

6. Where necessity exists for bringing the sulphur contents 
of cinders from iron pyrites (FeS a ) down to J to J per cent, to 
utilize the iron, or for the like treatment of rich gold-bearing 
sulphurets, the result is accomplished by the addition of a fire¬ 
place to the lower hearth. 

7. The average cost of calcining ores by this automatic fur¬ 
nace is not greater than by any other method at present in use. 

The cost of the furnace, complete, with power, is about the 
same as that of the equivalent grate-bar space in kilns, or equal 
burning space in the present type of shelf-furnaces. 

The following furnaces are in constant use: 


Grasselli Chemical Works at Cleveland. 10 

Beaver Falls. 4 

Titusville. 3 

Olean. 3 

Tremley’s Point. 6 

Bergenport Chemical Works. 5 

Wilmington, Delaware. 6 

Baltimore. 10 

Richmond, Va. 4 

Savannah, Ga. 4 

Total. 55 

and others now building. 


There are four of the latest type furnaces now working at 
the Parrot Copper Company’s plant, Butte, Montana. The 
average daily capacity of the furnaces running strictly for the 













144 MODERN AMERICAN METHODS OF COPPER SMELTING. 


manufacture of sulphuric acid is about 7,500 pounds of 45 per 
cent, sulphur ores. The furnaces at Butte are running on a low- 
grade copper pyrite not to exceed 35 per cent, sulphur, and the 
capacity is 14,000 pounds per day. A few of these furnaces 
have been built with five hearths instead of four hearths shown 
in the illustration, the benefit being solely the reduction of the 
amount of sulphur in the cinders to less than 1 per cent., but no 
corresponding increase in tonnage of ore. 

There are running at Bridgeport, Connecticut, one double 
furnace; at Gowanus Bay, Long Island, two double furnaces; at 
Elizabethport, New Jersey, two double furnaces; and others are 
building. 

The accompanying drawing shows a Hammond improved 
Spence furnace used at the great Treadwell mill, Douglas Island, 
Alaska, where a number of them are employed in roasting the 
gold-bearing concentrates for treatment by the Plattner chlorina¬ 
tion process; six double furnaces roast from 18 to 20 tons of 
concentrates a day to a “ dead roast,” with an expenditure of 
about ^ cord of wood per ton of ore. If the furnaces are used 
as pyrites burners or if the ore contains over 35 per cent, of 
sulphur, and 1 to 3 per cent, sulphur in the roasted product is 
not injurious, no fuel is necessary. The capacity in such cases 
is more than double the figures given above. An expert who 
has witnessed the working of these furnaces at the Treadwell 
mill says, u This furnace may take the place of the old rever¬ 
beratory, for it has all of its advantages and none of its draw¬ 
backs.” The space required is small and no skilled labor is 
necessary. Once adjusted, it will continually discharge a finished 
product. Two men on a shift can attend to six double furnaces 
easily. One keeps the hoppers full while the other keeps the 
temperature even. The fronts and backs of the furnaces are so 
arranged that the supply of ore can be regulated exactly. The 
dust is even less than in the old reverberatory. A substantial 
hydraulic cylinder moves the rakes, which are so arranged as to 
prevent the banking of the material at the ends of the furnace. 
The iron rails of the Spence furnace, which gave much trouble, 
are replaced in this by very hard brick tiles. With ordinary 
care the iron rakes will last six months when salt is used in 
roasting, and two years when it is not employed, and when burnt 
out can be replaced by new rakes in ten minutes. 


LONGITUDINAL SECTION OF SPENCE AUTOMATIC CALCINER 



K8:f- 















































































































































































































146 MODERN AMERICAN METHODS OF COPPER SMELTING. 

b. With movable hearth .—In this type of furnace, the slowly 
revolving hearth is of a circular and conical shape, and may con¬ 
sist of two or more stories, a series of stationary rakes being 
fastened above each in such a manner that the ore-charge is 
thoroughly stirred at frequent intervals. 

The Parke furnace and the Brunton ealciner are perhaps the 
best known specimens of this type, and have been somewhat ex¬ 
tensively used in England for desulphurizing purposes. Their 
great weight, cost of construction, and heavy repairs must cer¬ 
tainly go far toward counterbalancing the slight saving in labor 
claimed. 

IV. REVERBERATORY CALCINERS. 

a. With open hearth .—This division includes virtually all of 
the calciners in every-day use in this country for the calcina¬ 
tion of copper-bearing sulphides where neither the manufacture 
of sulphuric acid nor other outside issue has influenced the choice 
of apparatus. 

The essential features of the ordinary reverberatory ealciner 
are a hearth, heated by a fire-place, from which it is ordinarily 
separated by the bridge-wall, and accessible by certain openings 
through the side walls, the whole being covered by a flat arch 
against which the flame reverberates in its passage from the grate 
to the flue, thus being brought momentarily in contact with the 
ore spread upon the hearth, while the combined gases from fuel 
and charge pass into the open air through a chimney, in many 
cases first traversing a series of flues and chambers for the pur¬ 
pose of retaining such particles of metal as may have been either 
chemically or mechanically borne away by the rapid draught. 

A very small grate surface, as compared with the hearth area, 
distinguishes this type from the reverberatory smelting-furnace, 
and corresponds to the very moderate temperature suited to the 
process of calcination, permitting its almost entire construction 
of common red brick. 

A single detailed account of the longest and largest variety of 
ealciner in common use will serve as a model for all smaller speci¬ 
mens of the same class. 

The principal variable dimension of a copper-desulphurizing 
furnace is its length, as, for economical reasons, its width should 
always be as great as is compatible with convenient manipula¬ 
tion. Experience has placed this limit at 16 feet for the inside 



Four Hearth Calcining Furnace 



























































148 MODERN AMERICAN METHODS OF COPPER SMELTING. 

measurement of the hearth, nor should this dimension be lessened 
without good and sufficient reasons. 

The length of the hearth is limited chiefly by the capacity of 
the ore to generate heat during its oxidation, the immediate in¬ 
fluence of the fire-place being seldom capable of maintaining the 
requisite temperature upon a hearth over 16 feet in length, with¬ 
out resorting to the use of a forced blast, or of a draught so 
powerful as greatly to increase the loss in dust as well as the 
consumption of fuel. 

The importance of the heat generated by the oxidation of sul¬ 
phides in maintaining a proper temperature, and especially in 
conveying the heat to a great distance from the initial point, is 
seldom fully realized. Its intensity and durability depend upon 
the percentage of sulphur in the ore, and also not a little upon 
the manner in which it is chemically combined, the bisulphides 
—such as iron pyrites—furnishing a much greater amount of 
heat than monosulphides containing an equal gross amount of 
sulphur. 

An ore carrying less than 10 per cent, of sulphur will not 
furnish sufficient heat to warrant the addition of a second hearth 
to the first 16 feet, which will be assumed as the normal length 
of a single hearth. (Such a condition would scarcely occur in 
practice, as, under ordinary circumstances, any copper ore con¬ 
taining such a low percentage of sulphur could be smelted raw.) 
An increase of sulphur to 15 per cent., however, will be sufficient 
to heat the second hearth, while a 20 per cent, sulphur ore should 
work rapidly in a three-heartli furnace. The addition of a fourth 
and final section is rendered justifiable by the increase of the 
average sulphur contents of the ore to 25 per cent., and even a 20 
per cent, bisulphide charge may be worked to advantage in the 
same. 

The adoption of this method of roasting, by which the ore is 
fed into one end of the furnace, and gradually moved to the 
other extremity before discharging, is attended with several ob¬ 
vious advantages, among which are: The gradual elevation of 
temperature from a point compatible with the easy fusibility of 
the unaltered sulphides to that degree necessary for the complete 
decomposition of the pertinacious basic sulphates of copper and 
zinc; the great saving in fuel effected by thus obtaining the full 
benefit of the heat generated in the process of roasting itself • the 


CALCINATION OF ORE AND MATTE. 


149 


-certainty that the charge must undergo a certain number of 
thorough stirrings and turnings in its transportation over so ex¬ 
tended a space; the establishment of a fixed duty, which must be 
performed by the workmen, whose labor can thus be much more 
easily controlled than with the single-heartlied type of calciner, 
where the attendants can easily substitute an idle scratching for 
the vigorous manipulation necessary to move the ore forward 
promptly; a great simplification in firing, it being only necessary 
in the long furnace to maintain an even, high temperature, while 
with the single hearth, much experience and judgment are re¬ 
quired to adapt the heat to the ever-varying condition of the 
charge; lastly, a decided economy in construction, the ratio of 
fire-brick to common red brick for an equal capacity of plant 
being much less in the employment of long furnaces. 

As there seems to be almost no limit to the extent of surface 
over which the requisite temperature may be obtained in the cal¬ 
cination of highly sulphureted ores, it is very natural that exper¬ 
iments should have been made with still longer furnaces than 
any yet mentioned, 120 feet being the extreme inside length yet 
attempted, so far as known to the writer; but careful and re¬ 
peated trials have shown beyond a doubt that no sufficient ad¬ 
vantage is reaped to pay the increased cost of the inclosing 
building and other expenses of plant. It is not possible for two 
attendants properly to manage a furnace having more than four 
full-sized hearths, if the latter is pushed to its full capacity, while 
the addition of a fifth hearth demands a third laborer, whose 
time, however, will not be fully occupied, while a sixth hearth 
will overtax the three workmen. In short, the testimony of 
many excellent metallurgists, to which the author can add his 
own experience, unequivocally condemns the lengthening of or¬ 
dinary calcining-furnaces beyond the limits above indicated, ex¬ 
cepting under special and peculiar conditions. 

The number of working-doors to a long calcining-furnace, 
where the ore is moved from rear to front, should be as few as 
possible. The limit for comfortable work should not exceed eight 
feet between centers of doors, and any distance less than six 
feet is a decided disadvantage. 

The sides of the working-door frames should have short lugs, 
not exceeding six inches in length, cast on them, in order that 
they may be firmly held in position by the buckstaves, which are 


150 MODERN AMERICAN METHODS OF COPPER SMELTING. 

placed in pairs for this purpose, a single buckstaff being placed 
in the center of the space between each pair. The bottom of the 
door-frames should be on a level with the hearth surface, which 
should be three feet above the floor grade of the building, which 
should slope gradually upward toward the rear of the furnace, to 
correspond with the increased height of each succeeding hearth. 

The common practice of filling up the portions of the hearth 
between the working-doors with projecting, triangular masses of 
brick-work cannot be recommended, as valuable space is often 
sacrificed in this manner. Slight projections, as shown in the 
cut on page 147, may be built to fill the absolutely inaccessible 
angles; but with properly constructed door-frames, and careful 
manipulation on the part of the roasting attendants, but little 
waste area should exist, and this will regulate itself by becoming 
filled with ore, which may remain there permanently. This re¬ 
fers, of course, to the treatment of large quantities of low-grade 
ores, where slight inaccuracies resulting from the trifling mixture 
of ores can do no harm. 

After raising the side walls to the height required by the iron 
door-frames, usually about ten inches above the hearth level, the 
skewback for the main arch should be laid. This applies to the 
entire furnace from the beginning of the fire-box to the extremity 
of the rear hearth, and is a very simple matter, especially if the 
arch is to be perfectly horizontal, as is to be recommended in 
most cases. A taut fine should be stretched, to insure accurate 
work, and if red brick are used, they should be cut on one long 
edge, being laid, of course, longitudinally and on the fiat. They 
should be cut at an angle slightly greater than required by the 
curve of the arch, which should rise about three-quarters of an 
inch to the foot, making a sixteen-foot arch twelve inches higher 
in the center than at the sides. This rise, though less than is 
often recommended, will be found ample to insure perfect safety 
and durability, and will tend to spread the flame and heat toward 
the sides of the hearth. 

If so-called u side skewback ” fire-brick are within reach, they 
should be used in place of the red brick, saving much cutting and 
insuring a better job.- Three rows, in height, of red brick, or 
two of fire-brick, will give a solid bearing, the total number re¬ 
quired for a furnace of the size under consideration being respect¬ 
ively 600 and 375. 

«/ 


CALCINATION OF ORE AND MATTE. 


ir>i 


It is of sufficient importance to bear repetition, that all por¬ 
tions of the mason work above the hearth line, or wherever ex¬ 
posed to heat, must be laid in clay—common brick clay, tempered 
with sand, being quite good enough for all portions of the fur¬ 
nace—as fire-clay is usually expensive in the localities where 
copper ores abound. 

Lime mortar, much improved by the admixture of a little 
good cement—say 10 per cent,—may be advantageously em¬ 
ployed for the outside work, and wherever there is no danger of 
heat, as it makes handsomer and stronger work, and is greatly 
preferred by the masons, who require constant supervision to 
compel them to use clay mortar where it is necessary. 

The heavy iron bridge plate, so indispensable in reverberatory 
smelting-furnaces, may be entirely omitted, the bridge being built 
up solid and covered on the top and sides with fire-brick, with 
the exception of a longitudinal opening 3 by 8 inches, which 
should penetrate it from one end to the other, communicating 
with the outside air on each side of the furnace, and with the 
hearth by some half-dozen 2 by 4-inch openings. 

By this means, heated air free from all reducing gases is ad¬ 
mitted into the furnace below the sheet of flame that sweeps over 
the top of the bridge. The oxidizing effect of this current of air 
is very powerful, and, as frequently determined by experiment, 
hastens materially the calcining process. 

If wood is used as a fuel, an additional row of similar open¬ 
ings should be constructed in the arch, immediately over the 
front fine of the bridge-wall, by which a much more perfect com¬ 
bustion of the gases is effected. With coal as a fuel, the latter 
openings are superfluous, provided the firing is properly man¬ 
aged. 

Aside from the sixteen working-door frames, and the ordinary 
doors for fire-box and ash-pit, no castings are necessary for the 
entire structure, excepting a small frame to protect the charging- 
hole, which should be situated a little back of the center of the 
rear hearth, being placed, of course, in the medium longitudinal 
line of the furnace. It will add also materially to the durability 
of the fire-box to surround the portions of the same most exposed 
to pressure or mechanical violence by fight cast plates, held in 
place by the uprights. 

As the portion of the hearth immediately beneath the charging- 


152 MODERN AMERICAN METHODS OF COPPER SMELTING. 

hole is exposed to excessive wear from the constant precipitation 
of heavy masses of wet material upon it, an area some three feet 
square, and in the locality designated, should he constructed of 
either fire-brick 01 * slag blocks, the latter, from their texture and 
general physical condition, being peculiarly well suited to the 
purpose. 

By referring to the sketch on page 147, it can be plainly 
seen at what stage in construction the various bearing bars and 
other iron work must be inserted. 

It will be noticed that, instead of adopting the ordinary large 
ash-pit, entirely open at the rear, according to the invariable 
English practice, preference is given to a closed ash-pit, to which 
air is admitted by a door at one or both ends. This effects a 
great saving in fuel, and brings the process of combustion more 
perfectly under control. Comparative tests, extending over a 
considerable period of time, show this saving to amount to about 
50 per cent, of the entire fuel consumed, in the case of coal, and 
about 65 per cent, (in volume) when pine wood is used. The 
tight ash-pit becomes, of course, a matter of positive necessity 
where anthracite coal, with a forced blast, is used. 

The side and end walls having been carried up to the required 
height, and the skewback constructed on both sides for their en¬ 
tire length, the carpenters take possession temporarily, usually 
under the supervision of the head mason, to put in the wooden 
center on which the arch is to be built. If a second furnace, or 
indeed any other work, is available for the remaining masons, 
it is advantageous, though not indispensable, to permit the 
furnace to stand uncovered for several days, thus allowing the 
mortar to set, and greatly increasing the strength of the mason 
work. 

Having selected for description that pattern of calciner in 
which the gradual diminution of the space between arch and 
hearth, as it recedes from the grate, is due to successive slight 
elevations of the hearth level, instead of the ordinary downward 
pitch of the roof, it is evident that the arch throughout its entire 
extent will be horizontal, while all four inclosing walls are built 
up to the same height at every point, with the exception of a rec¬ 
tangular flue-opening in the rear wall, 6 by 30 inches. 

The construction of the wooden pattern or center is, therefore, 
extremely simple, requiring only some 20 pieces of 2-inch plank, 


CALCINATION OF ORE AND MATTE. 


153 


16 feet long and 14 inches wide • a lot of 2 by 4 scantling, to 
form posts about 10 inches in length, four of these being needed 
to support each plank on edge; and finally, a sufficient amount 
of 4-inch battens, from one-half to one inch thick, to cover the 
area of the required roof, when placed about three-quarters of an 
inch apart. The plank should be perfectly sound, and at least 
partially seasoned. 

By the aid of a long rod, moving upon a pivot at one end, 
while the free extremity carries a pencil, a segment of a circle 
corresponding to a rise of 12 inches in the center of the length of 
16 feet, should be struck on each plank, and the line followed ac¬ 
curately with a jig-saw. 

The segments for that portion of the arch over the bridge 
and fire-box are shorter, of course, than those belonging to the 
main hearth, but should be got out in the same manner, and then 
shortened at each end to the required length. 

The scantling should be cut into posts somewhat shorter than 
necessary to bring the curve on the upper edge of the segments 
to the proper height for the lower surface of the arch, so that 
each post may be wedged to an exact bearing with thin slips of 
wood. It is quite necessary that the weight should be evenly 
distributed, and each segment, when brought into correct posi¬ 
tion, is held there by driving a nail through a longitudinal line 
of battens in the center and at each extremity. 

The segments for sloping arches should be still further 
strengthened by short braces toe-nailed obliquely from the upper 
edge of one strip to the lower edge of its neighbor, and so on 
throughout the entire frame. 

An omission of this precaution has caused the canting of the 
segments and consequent destruction of a large, nearly completed 
arch under the author’s charge. 

No difficulty will be experienced in removing the wooden pat¬ 
tern in good condition for further use, provided it is supported 
on small posts as just described; but if long, heavy blocks of 
timber are used as a foundation for the segments, great labor as 
well as much injurious sledging must accompany their removal, 
resulting usually in the complete destruction of both segments 
and battens. In fact, where this method of support has been 
practiced, it will be found best to burn out the inclosed patterns, 
after the tie-rods are properly tightened, closing both damper and 


154 MODERN AMERICAN METHODS OF COPPER SMELTING. 


ash-pit so as to allow only a slow smoldering, and prevent any 
injurious rise of temperature in the still damp furnace. 

Few jobs of mason work require more care and conscientious¬ 
ness than the laying of a large caleiner arch, as, owing to its 
great width and slight curvature, a very little lack of closeness 
in its myriad joints would be sufficient to allow it to yield to the 
enormous pressure brought to bear by its own weight, and be¬ 
come sufficiently compressed to slip down between its side walls. 
It is quite a simple matter to lay a good solid arch of fire-brick, 
owing to their great regularity and smoothness and almost per¬ 
fect rectangular form; but when red brick are used, which vary 
so in size and thickness, and are so frequently warped out of all 
reasonable shape, much care is required. 

In ordinary ealciners, it is customary to construct that por¬ 
tion of the arch from the fire end of the furnace to a point mid¬ 
way between the first and second working-doors of fire-brick, 
nine inches in thickness, the brick standing endwise. At this 
point, or even considerably sooner, when necessary, red brick are 
substituted, being placed also on end, each brick, after being 
dipped into a pail of liquid clay mortar, being pressed closely 
against its neighbor, and finally settled into position with a few 
light blows of the hammer. 

Moderately soft brick are, as a rule, best suited to this pur¬ 
pose, although they must, of course, possess ample solidity to re¬ 
sist the compression to which they are exposed. Hard-burned 
brick, though stronger, are too irregular and warped to be often 
used in a large arch, and in any case the brick should be all 
carefully selected beforehand by the attendant, and assorted in 
such a manner that each longitudinal row—extending the entire 
length of the furnace—is composed of brick of about the same 
thickness. 

Another most important precaution is the preservation of the 
proper angle, as, in order to establish the required curve, each 
row must incline slightly from the vertical, the lower end of the 
bricks being in contact, which is not the case with their upper 
extremities. 

The establishment and preservation of the proper curvature 
are facilitated by the occasional interpolation of a longitudinal 
row of wedge-shaped or key-brick, technically called “ bullheads.” - 
These are usually only obtainable made from fire-clay, but are 



CALCINATION OF ORE AND MATTE. 


155 


almost indispensable for the center row, when the final keying 
of the arch is effected. Otherwise, the entire row of key-brick 
must be cut from common brick, an arduous and imperfect task. 

The keying is a matter of some delicacy, and should be per¬ 
formed by a single workman, who should select or cut his keys 
of such thickness as to produce a uniform moderate pressure 
throughout the entire distance, no more force being exerted to 
drive the key into place than can be easily effected by a light 
mason’s hammer, using an intervening block of wood to prevent 
the destruction of the brick. 

While the masons are thus employed, the blacksmith and his 
helper should have completed the buckstaves and tie-rods from 
measurements furnished by the foreman mason as the work pro¬ 
gresses, it being in such cases easier to suit the length of the tie- 
rods to the completed mason work, than to pursue the opposite 
course. 

As soon as the arch is completed, the head mason and black¬ 
smith should proceed to the ironing of the furnace, which, with 
the assistance of two laborers, should be completed in a single 
day. 

The most convenient and easily obtained buckstaves in most 
cases are old iron rails of full size, say, 80 pounds to the yard. 
Properly shaped I-beams, of corresponding strength, are about 15 
per cent, lighter. The tie-rods may consist of one inch round-iron 
for the bottom rods, and one inch and a quarter iron for the upper 
rods. The lower rods are already long in place, and through 
each of their loops should now be slipped one of the upright 
buckstaves, cut to the proper length, and temporarily wedged 
into the loop to keep it perpendicular. 

The upper tie-rods may be made the same as the lower, with 
a loop at each end—the necessary tightening being effected by 
flat-iron wedges; or they may have a threaded extremity at one 
end passing through a corresponding hole in the buckstaff, and 
fitted with a strong nut; or, best of all, a small ring is formed at 
one end of the tie-rod, through which slips a U-shaped piece of 
round iron, which fits against the buckstaff, on the other side of 
which a piece of flat iron, pierced with two holes for the free ends 
of the U, is held, these ends being threaded j a nut for each of 
the ends completes the apparatus, and presses the piece of flat 
iron tight against the upright. This is a simple and highly sat- 


156 MODERN AMERICAN METHODS OF COPPER SMELTING. 

isfactory device, and avoids the disagreeable process of wedging 
in the one case, or of punching a large hole through a narrow 
rail in the other. The strain is distributed over two bolts and 
nuts, and can be instantaneously increased or diminished; nor 
will the nuts rust solid into place, provided they are saturated 
with oil annually, and slightly turned, to free them. 

Whatever method of tightening the tie-rods may be selected, 
the process of ironing or anchoring should begin with the first 
tie-rod on the main body of the furnace, nearest the fire end, and 
proceed systematically toward the rear, thence returning to the 
shorter transverse rods that support the arch over the grate, and 
terminating with the long longitudinal rods, which, for conven¬ 
ience of handling, should be in three lengths, connected with 
hooks and eyes. Up to this time, no great strain should be put 
upon the rods, everything being merely brought to a solid bear¬ 
ing ; but after all are in place, and the buckstaves evened both 
vertically and laterally, the rods may be drawn to the desired 
tension, the skewback being still further supported by a bar of 
one by four inch flat iron, or, better, an iron or steel rail, let in 
flush with the brick-work. 

This is largely a matter of experience, and being of vital im¬ 
portance, should receive the most careful attention on the part of 
the builder, as too lax a condition of the rods may permit the 
entire falling in of the arch, while the contrary fault may cause 
a positive buckling and elevation of the same, accompanied with 
a general cracking and distortion of the lateral walls. The latter 
accident, in a moderate degree, is much more likely to occur than 
the former, owing to the natural tendency to overdo a measure 
essential to safety, and yet not exactly defined. 

The lateral rods should be tightened until they begin, when 
struck near the center with a hammer, to vibrate rapidly, and to 
be but little depressed when stepped upon. (It is almost need¬ 
less to say that none of the upper rods should touch the arch.) 
A simultaneous examination of the brick-work forming the up¬ 
per portion of the side walls should also be made, as it is here 
that the effect of the curving of the buckstaff from too great 
tension, and consequent pressure against the mason-work, is first 
visible. 

The extreme limit of tension is reached when the first signs 
of this appear, as nothing can be gained by bending the uprights,, 


CALCINATION OF ORE AND MATTE. 


157 


and if the latter are sufficiently strong and applied in the num¬ 
bers shown in the illustration, the arch may be considered per¬ 
fectly supported. All the rods should be tightened to about the 
same extent, although it must be remembered that the great 
length of the longitudinal rods may prove deceptive in estimat¬ 
ing their tension, it being impossible to tighten them to such a 
degree as the shorter lateral ones. 

A single additional precaution is recommended, though sel¬ 
dom practiced by builders. This consists in breaking up a few 
thin roofing slates into fragments a couple of inches in length, 
and driving these with moderate force into whatever crevices 
may still be found in the surface of the arch. 

Some twenty or thirty pails of liquid mud are now poured 
over the arch, and the process repeated as it dries, until every 
crack and crevice is filled, and the roof rendered completely solid 
and air-tiglit. 

The wooden center on which the arch was built should now 
be removed by first knocking away the little posts that support 
it, using a light stick of timber as a battering-ram, and proceed¬ 
ing from one side door to the next until every stick and batten are 
removed. They should be stored for future use. Any indica¬ 
tions of settling on the part of the arch must be immediately 
counteracted by tightening the tie-rods; but when the precau¬ 
tions enumerated have been carefully observed, this can never 
occur. 

The length of time the completed furnace may now stand un¬ 
touched with advantage to the mason-work is only limited by the 
requirements of the business, which almost invariably require its 
being put in commission at the earliest possible moment. Under 
such circumstances, a smoldering fire of large logs, knots, or any 
slow-burning waste material, should at first be kindled on the 
floor of the ash-pit, the grate-bars not being put in place until 
the masonry surrounding the fire-place is partially dried. 

In twelve or eighteen hours, the fire is elevated to its proper 
place, and with a nearly closed ash-pit door and partially lowered 
damper, the process of drying proceeds gently and without that 
violent generation of steam and vapor that is sure to be accom¬ 
panied by extensive Assuring of the brick-work and permanent 
weakening of the entire structure. 

A most careful and repeated examination of the condition of 


158 MODERN AMERICAN METHODS OF COPPER SMELTING. 


tie-rods and buckstaves should be made every twelve hours from 
the first kindling of the fire until the furnace has attained its full 
heat, and may be supposed to have expanded to its utmost limits, 
although it may be a month or more before all evidences of move¬ 
ment cease. The first indication of this process will be seen in 
the neighborhood of the bridge and fire-place, where the highest 
temperature prevails. A bending of the buckstaves, combined 
with a pressing in of the skewback line and an increased tension 
of the cross-rods, are warnings that may soon be followed by 
either a complete giving way of some portion of the iron-work, 
or more frequently by a bodily upheaval of the arch and general 
Assuring of the brick-work, unless relieved by diminishing the 
strain to a corresponding degree. This process of loosening must 
be extended to the entire iron-work of the furnace, and continued 
as long as necessary, the tension being again increased if the fur¬ 
nace is ever allowed to cool down to any considerable degree—an 
operation more destructive to it than many months of ordinary 
wear. 

While the apparatus is thus gradually being brought into 
proper heat, the sheet-iron hopper should be suspended from tim¬ 
bers resting upon the trussed beams of the building. It should 
be strongly constructed and well braced, and provided with a 
stout lever, easily accessible to the operator when standing upon 
the floor of the building. A track running transversely to the 
row of calcining-furnaces, and parallel with the longitudinal axis 
of the building, renders these hoppers easily accessible to the car 
in which each weighed charge of ore is brought. The car is pro¬ 
vided with a dumping arrangement, so that it easily and com¬ 
pletely empties itself into the furnace hopper. The laborer who 
weighs and transports the charges can supply six furnaces, pro¬ 
vided everything is arranged as herein described, or in a similarly 
judicious manner. 

The outfit of tools may also now T be prepared, and should con¬ 
sist, for each four-hearth calciner, of 6 rabbles, 4 inches by 10 
inches and 12 feet long; 6 paddles, 8 inches by 12 inches and 12 
feet long; 4 door-hooks, to handle the sheet-iron working-door; 
1 long-hooked and pointed iron poker for wood, or an ordinary 
coal poker, if coal is used; 2 ordinary long-handled, square- 
pointed shovels; 1 scoop-shovel (for coal). 

The iron rollers, usually employed as rests for the long tools 


CALCINATION OF ORE AND MATTE. 


159 


at each working-door, soon lose their shape and cease to revolve. 
It is better, therefore, to provide merely a smooth iron bar, which, 
if kept well soaped, renders the handling of the tools as easy as 
any of the more expensive devices. 

When available, a free-burning semi-bituminous coal forms 
the most economical fuel for calcining purposes, but should 
always be burned upon a comparatively shallow grate, instead of 
using the deep clinker bed, so suitable to the smelting process. 
At the comparatively low temperature suited to calcination, the 
generated gas does not burn perfectly, and a great waste of fuel 
occurs. Coal should be fed at short intervals—from 30 to 45 
minutes—in quantities seldom exceeding 50 pounds. When 
wood is cheap, nothing can excel it as a fuel for calcining pur¬ 
poses, its long, hot, non-reducing flame being peculiarly suited to 
the requirements of the process. About one and two-thirds cords 
of hard, or two cords of soft, wood are commonly considered 
equal to 2,240 pounds of good bituminous coal. 

CONSTRUCTION OF FURNACE STACKS. 

While the furnace is gradually getting into condition for its 
first charge of ore, an opportunity is offered to return to the 
question of construction again, and describe a method of build¬ 
ing stacks that is much more economical than that usually pur¬ 
sued, and which, though not new or original, is certainly not 
generally adopted in the erection of smelting-works. 

Owing, perhaps, to the influence exercised by studying the 
practice of most European builders, and by following former cus¬ 
toms wdthout thinking particularly of the possible opportunities 
for improvement, the vastly greater number of furnace stacks 
now erected are very much more costly than they need be, both 
as regards labor and material. From a very recent comparison 
of costs with professional friends, the author has found that the 
average calciner stack, as erected by him during the past tw r elve 
years, has cost less than one-half the amount ordinarily ex¬ 
pended, making it worth wiiile to occupy a few paragraphs in de¬ 
scribing the more economical practice. 

The most important feature of a chimney is its foundation; 
but it is at this very point that a great saving over ordinary 
practice may be effected without lessening the stability of the su¬ 
perstructure. 


160 MODERN AMERICAN METHODS OF COPPER SMELTING. 

A mere increase in depth below the loose soil forming the sur¬ 
face of the ground does not add in the slightest to the value of 
the foundation, after a proper material for the same has once 
been reached; and as this occurs in the greater number of cases 
within three or four feet of the surface, the frequent practice of 
additional excavation for the apparent purpose of merely gaining 
depth is money thrown away. 

After removing the loose surface soil, and penetrating below 
any danger of frost, in the greater number of cases no advantage 
would be gained by excavating to a depth of 50 feet, unless solid 
bed-rock were reached. 

Any kind of gravel, hard-pan, or even soft loam or sand, if 
homogeneous, will answer the purpose perfectly, it being under¬ 
stood that reference is here made to an ordinary calciner or 
smelter stack not exceeding 80 feet in height. 

In the case of a yielding sand bottom, and especially if the 
hue of division between two strata of varying quality happens to 
cross the excavation, it is well to form a solid floor to the pit by 
putting in a double layer of three-inch plank, nailed cross-wise 
But in all ordinary cases the hole should be simply filled with 
broken stone, about the size of ordinary road metal. This ma¬ 
terial, when well rammed into place and thoroughly grouted, by 
pouring in a sufficient quantity of mortar composed of one part 
each of lime and cement, and three of sand, makes a foundation 
infinitely superior to one formed of a few large stones, the slight¬ 
est settling of any one of which will throw the chimney out of 
perpendicular. 

The excavation should be at least tw r o feet larger in every 
direction than the base of the chimney, and the stone-work of the 
latter, laid in lime and cement, should cease some three feet be¬ 
low the surface, at which point the brick-work usually begins. 

If a cupola smelting-furnace is in operation in the immediate 
vicinity, nothing can be more satisfactory or economical than the 
following plan, pursued by the author on several occasions: 

An excavation being made of the usual size, the molten slag 
from the smelting-furnace is wheeled to the spot in the usual 
movable slag-pots, and poured at once into the hole, which, when 
filled to the proper height with the fused rock, and leveled by 
means of little clay dams along the edges, so as to present a 
smooth surface for the masons to begin on, will contain a solid 


CALCINATION OF ORE AND .MATTE. 


161 


block of lava, weighing many tons, and as immovable as a ledge 
of rock. 

In constructing a stack, we have to determine the size of Hue 
desired, and intimately connected with the same is the degree of 
batter , or taper, which shall be given to the structure. 

The object of this batter is two-fold: 1st. For appearance. 2d. 
For the sake of strength. The first reason may be entirely neg¬ 
lected in metallurgical architecture, and experience has shown 
that, within the limit of height mentioned, a batter of one-eighth 
of an inch to the foot is ample. Nor need the taper be begun 
until the stack rises above the roof, as that portion of the struct¬ 
ure within the building is amply protected from the force of the 
wind. 

By thus decreasing the amount of taper, we greatly increase 
the capacity of the stack, as experience shows that a contraction 
of the flue in its upper portion is accompanied with a correspond¬ 
ing diminution of draught, while a positive enlargement of the 
same toward the top has a most beneficial influence. This latter 
point is gained by lessening the thickness of the chimney walls 
as they grow higher, while the outside taper remains constant. 

All calculations and formulae regarding the necessary size of 
any flue for a given duty have been found so greatly modified by 
circumstances—such as variations of internal and external tem¬ 
perature ; humidity of atmosphere and state of barometer; 
change of winds, etc.—that it is found safest to rely upon experi¬ 
ence and analogy; and after beginning with a much larger flue 
for safety, the author has finally found a stack 42 inches square 
inside, at its narrowest part, and 65 feet high, to possess ample 
capacity for two large calcining-furnaces such as just described. 
It is proper to add that a much smaller stack will produce the 
draught usually considered as quite sufficient for the calcining 
process; but long-continued experiment has shown such extraor¬ 
dinarily favorable results, as regards both capacity and perfection 
of roast, to arise from greatly increasing the ordinary calciner 
draught, that a sharp and powerful draught appears as essential 
to a calciner as to a smelting-furnace. 

For this reason, also, no more than two furnaces should be 
led into a common stack, it being almost impossible properly to 
equalize the admission of air to each calciner, and to produce 
that sharp and vigorous draught so essential to rapid oxidation, 


162 MODERN AMERICAN METHODS OF COPPER SMELTING. 


and especially to the conveyance of the sheet of flame and heated 
gases over the whole length of a 1-hearth calcining-furnace. The 
interposition of dust-chambers, or preferably of large flues, filled 
with parallel rows of sheet-iron, according to the method found 
so efficient and economical at Ems, is of course necessary, and 
should be present in any case.* Limited experiments conducted 
by the author fully satisfy him of the great benefit to be derived 
from the adoption of this economical and efficient method of con¬ 
densation. 

The size of chimney mentioned—42 inches-—will answer for 

•/ 

all elevations up to 5,000 feet above sea-level. For each 1,000 
additional height, these figures should be increased one inch. 

For a calciner chimney of this size and 65 feet in height, the 
walls at the base should be 17 inches thick, the length of two red 
brick, no fire-brick being needed, as the gases are sufficiently 
cooled by their passage through the long furnace and flue. This 
thickness is maintained for a height of 25 feet from the ground, 
which brings it somewhat above the roof of the building. At 
this point, the external batter of one-eighth of an inch to the foot 
is begun, and an internal set-off of 4 inches is taken; thus de¬ 
creasing the thickness of the walls to 13 inches, and enlarging 
the flue to 50 inches. 

This constant taper is maintained by the employment of an 
ordinary beveled plumb-bob, which obviates any trouble or cal¬ 
culation. This condition of affairs is continued for another 25 
feet, during which distance the flue is contracted to a size of 
about 44 inches, when another internal 4-inch set-off is taken, in¬ 
creasing the same to 52 inches, while the walls are diminished to 
8 inches. 

This, being continued for 15 feet, gives the full height of 65 
feet, the flue at the top being still 48 inches square, or 6 inches 
larger than at the base. No ornamental finish at the top should 
ever be allowed, the stack either being surmounted by a light 
casting to hold the brick in place, or left without this protection, 
the iron braces being usually sufficient to prevent the loosening 
of the upper rows of brick-work. An ornamental cap is simply 
a source of annoyance and danger, and should never be permitted 
in a stack devoted to the passage of sulphurous vapors. 

* See description of Ems method of condensation, by Professor Egleston, 
in Transactions of the American Institute of Mining Engineers , xi., 379. 






CALCINATION OF ORE AND MATTE. 


163 


A chimney of this size is best built from the outside, a scaffold 
being erected by placing eight stout poles about the base of the 
proposed structure, nailing cross-pieces at the proper height for 
the plank staging, and thoroughly bracing the uprights by 
boards nailed diagonally from one to the other. 

The uprights may be lengthened out almost indefinitely by 
careful splicing, and as the stack grows higher, new cross-pieces 
are spiked every five feet, and men and material thus maintained 
at the desired elevation. A rope and bucket, with a single 
wooden block fastened to the railing of the staging, and manip¬ 
ulated principally from the ground level, form the most econom¬ 
ical means of elevating the requisite material, while a single 
laborer above is able to furnish four masons with brick and mor¬ 
tar, most of the work being done from below. It is best to em¬ 
ploy four masons, so that one can work on each wall of the 
stack, and their position should be changed twice daily, in order 
to equalize any differences in the amount of mortar used, etc. 

Like all other mason-work that is to be exposed to heated sul¬ 
phurous gases, the interior portion of the stack must be laid in 
clay mortar (ordinary sticky mud); while the remainder of the 
structure should be laid in lime mortar, on account of its superior 
tenacity. To prevent the penetration of the vapors into the 
porous brick, the interior of the flue, should be thoroughly plas¬ 
tered with clay throughout its entire extent. 

While the durability of a chimney of this description is largely 
dependent upon its being ironed, it is still more dependent upon 
its not being ironed too stiffly. A stack with corners thoroughly 
inclosed in stiff angle iron, tightly held together with frequent 
braces, will fissure and give out in a few years, while a similarly 
built chimney containing a few light irons merely to hold the 
brick-work in place, will last from twenty to forty years. 

This is the result of personal experience, confirmed by the ob¬ 
servations of most other constructing engineers, and is especially 
the case in countries where high winds and violent fluctuations 
of temperature are prevalent. 

Eight uprights of g-inch by f-incli iron, each upright being 
placed about 4 inches from each corner of the stack, and passing 
through rectangular openings cut in h by 2-inch flat iron, which 
latter pieces are laid in the brick-work from 30 to 36 inches 
apart, are amply sufficient for the purpose. The holes must be 


164 MODERN AMERICAN METHODS OF COPPER SMELTING. 

so punched that the uprights can be wedged tightly against the 
brick-work, which is thus held in place even after the mortar has 
long succumbed to the combined influence of the roast gases and 
the elements. As a striking example of the accuracy of the 
above remarks, the reverberatory smelter stacks of the Detroit 
Smelting Company’s copper-refining furnaces at Lake Superior 
may be mentioned, where, on building a strongly ironed stack, 
they found it fissure and become unsound in a very short time; 
whereas their ordinary stacks, anchored only by means of occa¬ 
sional straps of flat iron built into the chimney walls and bent 
over at each end, have stood for fifteen years or more without 
showing crack or imperfection. 

A row of headers should be introduced at about every eighth 
-course, and the lower portion of the stack into which the two cal- 
ciner flues enter on opposite sides should be divided by a 4-inch 
partition wall into two equal compartments. This wall, extend¬ 
ing some five feet above the entrance flues, serves to bend each 
current in an upward direction, and thus prevent the whirl and 
disturbance of draught resulting from the meeting of two oppos¬ 
ing currents. 

The following interesting observation has been communicated 
by Messrs. Cooper and Patch, superintendent and chemist of the 
Detroit Refining-Works : 

In most reverberatory furnaces, the flue enters the stack at 
some distance above its base, and consequently there is a cavity 
inclosed by the chimney walls, of greater or less depth below the 
embouchure of the flue. When this apparently useless cavity has 
become filled up from the falling in of the stack fining, drippings 
from the molten brick, or other causes, the draught at once 
suffers and the capacity of the furnace is greatly diminished. 

Whether this phenomenon arises from the loss of the elastic 
air-cushion that is normally present, or whether there is some 
other reason, the fact remains, and although the observations 
have been confined mostly to smelting-furnaces, it is probable 
that a calcining-furnace may be affected in a similar manner, and 
therefore, in all cases where a horizontal or inclined flue enters a 
stack, it should be so constructed as to leave an open space of 
from 4 to 6 feet below it. This need not communicate with the 
outside an* in any way, except for the purpose of cleaning the 
stack or entering it for repairs. 


CALCINATION OF ORE AND MATTE. 


1G5 


It is well to provide every high stack with a good lightning- 
rod, properly fastened and insulated. 

The building that covers any considerable number of calcin¬ 
ing-furnaces is necessarily of great extent, and should, if pos¬ 
sible, be built of very light and, at the same time, fire-proof 
materials. 

Scarcely anything fills these requirements so thoroughly as a 
medium grade of corrugated iron. This, if well fastened down, 
and painted every three or four years, Mill be found the most 
economical and satisfactory material for both sides and roof that 
is yet known. If the number of furnaces under a single roof 
exceeds two, they should be placed at right angles to the greatest 
length of the building, a space of only three feet being left be¬ 
tween the rear end of the furnace and the corresponding side of 
the building, while between the fire-box and the lower side of the 
building there should be ample room for a drive-way for the 
conveyance of fuel, as well as for a railroad paralled to the same 
and close to the wall, over which the calcined ore may con¬ 
veniently be dumped into a paved and roofed inclosure on a level 
as low as the circumstances of the case permit. The sixteen-foot 
calciners should be separated by spaces of at least fourteen feet. 

As the main building for these long calcining-furnaces must 
be from eighty to ninety feet in width, it is often the practice to 
support the cross-beams on posts that, if properly placed close to 
the furnace and midway between the working openings, need not 
interfere with the long tools in use. But there is no difficulty in 
constructing trusses to support a roof of this size without the aid 
of posts, nor need the expense be much greater. The principal 
difficulty is encountered in raising these immensely long and 
heavy “ bents; ” but this may be entirely obviated by construct¬ 
ing a series of cheap scaffoldings, and putting them together 
piece by piece, instead of attempting to raise the entire “ bent ” 
bodily. The ridge of the roof should be surmounted by a contin¬ 
uous ventilator throughout its entire extent. The details of this 
work may be intrusted to any experienced carpenter. 

COST OF CONSTRUCTION OF CALCINING-FURNACE. 

The following estimates of cost are taken from notes that 
cover the construction of a considerable number of large calcin¬ 
ing-furnaces, and being given without alteration or omissions, ex- 


166 MODERN AMERICAN METHODS OF COPPER SMELTING. 

cepting the necessary reduction to our assumed standard of costs, 
should furnish reliable figures on which to base future plans: 

COST OF ONE FOUR-HEARTH CALCINER. 

Excavation—45 days at $1.50. $67.50 

Removal of material excavated. 35.00 

Superintendence and miscellaneous. 24.00 $126.50 

Foundation walls—1,840 cubic feet. 

2,000 slag-brick at 2 cents. 40.00 

20 days stone-mason and helpers. 120.00 

Materials for mortar. 28.00 

Labor on same and utensils. 16.00 

Miscellaneous labor. 12.00 

Superintendence. 15.00 $231.00 

Brick-work on furnace proper. 

2,420 cubic feet, say 50,000 red brick at $8. $400.00 

7,500 fire-brick at $40. 300.00 

Lime and sand. 137.00 

4 tons fire-clay at $8. 32.00 

8 tons brick-clay at $1.50. 12.00 

32 loads sand at $1.50. 48.00 

112 days’ brick-masons’ labor at $4. 448.00 

112 days’ ordinary labor at $1.50. 168.00 

3 days’ carpenters’ labor at $3. 9.00 

Miscellaneous labor. 35.00 

8 days, blacksmith and helper. 40.00 

Materials consumed by same. 8.00 

Iron work. 

Superintendence. 112.00 $1,749.00 

66 buckstaves (old rails), 6f feet long, 80 pounds, at If 

cents per pound. $85.80 

Tie-rods and loops, 2,056 feet, lf-inck round iron = 8,327 

pounds, at 2 cents. 166.54 

Flat iron for skewback, grates, etc. = 2,064 pounds, at 2 

cents. 41.28 

16 cast frames and doors, at 156 pounds each = 2,496 

pounds, at 2f cents. 62.40 

Fire-doors and other small castings. 16.50 $372.52 

Nuts and bolts. 6.25 

Short flue, with damper and f cost of stack. 364.00 

Grading and miscellaneous. 47.50 

Tracks for feed and discharge of ore. 62.40 

Set tools, complete, as per former schedule, 1,250 pounds, 

at 2 cents. 25.00 

Labor on same. 18.00 

One iron ore-car (list price). 85.00 

Grand total.,. $3,087.17 






































CALCINATION OF ORE AND MATTE. 


167 


The repairs on a thoroughly built calciner should be nothing 
for the first three years; for the succeeding seven years, they will 
average 3 per cent, per annum on its first cost, while from its 
tenth to its fifteenth year, 5 per cent, per annum will probably 
be expended in renewing the hearth and roof once and patching 
the furnace in various places. 

After fifteen years of constant usage, it is cheaper to build a 
new furnace than to keep the old one in repair; but few metal¬ 
lurgical enterprises in this country require to provide for a period 
longer than the above. 

The variety of reverberatory calciner known as the muffle fur¬ 
nace is now seldom used by the copper smelter, as, except for 
purposes of acid manufacture, it possesses few advantages above 
the ordinary hearth variety, and in case this branch of metallurgy 
is also practiced, some of the newer forms of automatic furnaces 
have displaced the muffle. The high cost of construction and 
greater consumption of fuel are also adverse to its employment, 
and although, from its gentle and regular heat, it possesses de¬ 
cided advantages in the treatment of easily fusible substances, it 
is rather suited to the calcination of matter containing much 
lead, or of pyrites with salt, as in the Henderson process, none of 
which operations comes within the scope of this treatise. 

An easily fusible ore can be very efficiently protected from 
the fierce heat of the first hearth of an ordinary calciner bv the 
construction of a four-inch curtain arch, covering one-third or 
more of its surface from the fire-bridge onward, though such a 
precaution is seldom necessary, excepting in the case of matte 
calcination, which requires but slight modifications of the roast¬ 
ing process as applied to ordinary sulphide ores. 

The process of ore calcination, like most other operations 
based on chemical reactions, must be understood before it can be 
properly and intelligently executed, and no description of the 
same would be complete without a brief review of the chemistry 
of the calcining process. 


CHAPTER VIII. 


THE CHEMISTRY OF THE CALCINING PROCESS. 

A sufficient idea of the chemical reactions that occur in this 
important metallurgical process may be obtained by following 
an ordinary pyritous ore in its passage through the roasting-fur- 
nace, and carefully noting all the changes that it undergoes from 
the moment of its introduction until it is ready for the succeed¬ 
ing fusion; nor are the conditions in either roast-heaps or stalls 
so different as to require any separate consideration. 

A typical ore for this purpose might consist of a large pro¬ 
portion of pyrite, say 45 per cent., some 20 per cent, of clialcopy- 
rite (containing about one-third copper), with a slight admixture 
of zinc-blende, galena, and sulphide of silver, while the remainder 
of the ore would usually consist of quartz or siliceous material, 
which may be regarded as practically inert in its effect upon the 
process of calcination. A charge of such ore, being introduced 
upon the hearth of a roasting-furnace still at a bright red heat 
from the preceding operation, exerts a powerfully cooling influ¬ 
ence upon the glowing brick-work, and within ten or fifteen 
minutes reduces the temperature to a point below the ignition- 
point of sulphur, the ore at the same time giving off its moisture, 
and gaining so much heat that a very slight aid from the fuel on 
♦ the grate is sufficient to start the oxidation of the iron pyrites, as 
shown by the blue, flickering flame that plays over the surface of 
the charge, beginning at that portion of the same that borders on 
the already hot charge occupying the adjoining hearth, and 
gradually advancing toward the rear, until every square inch of 
surface is in a state of active combustion. The rapidity of this 
process of oxidation varies according to the degree of tempera¬ 
ture and the sharpness of the draught, but should not occupy 
more than an hour from the first introduction of the charge. 
The composition of iron pyrites (FeS 2 ) is such that, while one 
atom of sulphur is united to the iron with considerable tenacity, 


THE CHEMISTRY OF THE CALCINING PROCESS. 


169 


the second atom is held by very feeble bonds, and becoming vol¬ 
atile at the moderate temperature of the calcining-furnace, unites 
with the oxygen of the air, forming sulphurous acid (S0 2 ), which 
escapes in the form of an invisible gas. This reaction is accom¬ 
panied by a very considerable evolution of heat and the flicker¬ 
ing blue flame already mentioned. Being entirely dependent 
upon the oxygen derived from the air, this reaction is confined 
principally to the surface of the charge, which, if left undisturbed, 
would soon undergo a slight fusion, causing a caking of the ore, 
and still further hindering the extension of the process. It is 
therefore just at this point that the necessity for frequent and 
vigorous stirring becomes strikingly apparent. By this manipu¬ 
lation, any incipient crust that may have formed is broken up, 
the temperature of the layer of ore is equalized throughout its 
entire depth, and fresh particles of ore are constantly exposed to 
the influence of the air. 

The stirring should begin on the first appearance of the blue 
flame, and continue for ten minutes at a time, with equal inter¬ 
vals of rest, during which time the working openings should be 
closed, while an ample air supply is admitted through the regular 
channels provided for this purpose. The stirring should take 
place from both sides of the furnace at the same time, and should 
be systematic, vigorous and thorough-, extending to the very 
bottom of the charge, and omitting no portion of the ore. 

During this period of roasting, and until the disappearance of 
the blue flame, the roast gases consist almost exclusively of sul¬ 
phurous acid together with steam from the moisture present, and 
the invariable products of the combustion of the fuel. 

It will, of course, be understood that the S0 2 and other roast 
gases form but a small proportion—seldom more than 2 per 
cent.—of the air issuing from a calciner stack; atmospheric air 
always being present in overwhelming proportions. The S0 2 re¬ 
sults from the direct oxidation of one atom of the sulphur con¬ 
tents of the iron pyrites, or, when the temperature is somewhat 
high, of the absolute volatilization of this atom of sulphur as sul¬ 
phur, and its immediate combustion to S0 2 . 

The next stage of the process may be reckoned from the be¬ 
ginning of the oxidation of the iron of the pyrites, and also of 
its second atom of sulphur. This is a much less rapid and vig¬ 
orous process than the preceding, and is attended by the forma- 


170 MODERN AMERICAN METHODS OF COPPER SMELTING. 


tion of a certain amount of sulphuric acid, in addition to the sul¬ 
phurous acid, which is still generated in large quantities. The 
means by which the former acid was produced was not clearly un¬ 
derstood until Plattner’s patient and ingenious researches de¬ 
veloped the u contact theory/’ according to which sulphurous acid 
and the oxygen of the air, in the presence of large quantities of 
heated quartz, or other neutral material, combine to form sulphuric 
acid, which may escape invisible, or in the form of white vapors 
when hydrated, or may in the instant of its formation combine 
with any strong base that may be present. 

In the case under consideration, protoxide of iron (FeO), aris¬ 
ing perhaps from the very particle of pyrites whose oxidation 
gave rise to the sulphuric acid, is at hand; and while the greater 
proportion of the sulphuric acid formed escapes into the atmos¬ 
phere, a certain amount combines with the protoxide of iron to 
form ferrous sulphate, whose presence may easily be detected, 
owing to its solubility in water. 

From the very commencement of the formation of sulphuric 
acid, a new and powerful oxidizing agent is gained, as the pro¬ 
tosulphate of iron is easily broken up by heat. The decompo¬ 
sition of its acid into S0 2 and O promotes the oxidation of other 
sulphides present to sulphates, while the protoxide of iron is 
raised to the sesquioxide of that metal—a tolerably stable com¬ 
pound, and one usually found in large quantities in thoroughly 
roasted pyritic ores. Before the complete decomposition of the 
ferrous sulphate has occurred, and indeed while some consider¬ 
able proportion of sulphide of iron may yet remain, an analogous 
process takes place with the chalcopyrite, its ferruginous portion 
following almost precisely the same course as the iron pyrites, 
while its copper contents are transformed into cupric sulphate, 
which, on the addition of water, becomes copper vitriol, easily 
recognized by its color and by several simple and well-known 
tests. 

As the process continues, and the temperature is gradually 
raised, this salt also undergoes decomposition, yielding at first a 
basic sulphate of copper, which, upon losing its acid, becomes a 
dioxide and eventually a protoxide of that metal. These last 
changes, however, require a protracted high temperature. 

The oxidation of the iron present is pretty well advanced at 
the time of the maximum formation of cupric sulphate; but it 


THE CHEMISTRY OF THE CALCINING PROCESS. 171 

is not until the decomposition of at least 75 per cent, of the last- 
named salt that the formation of sulphate of silver begins with 
any considerable energy. When once fairly started, however, 
this interesting and important reaction progresses with great 
rapidity, and the decomposition of the comparatively large pro¬ 
portion of sulphate of copper present furnishes ample oxidizing 
influence for the minute quantities of sulphide of silver. The 
maximum formation of the latter substance usually coincides 
with the almost entire destruction of the former salt, and it is at 
this point that the Ziervogel calcination should terminate, as any 
further exposure of the silver salt to heat lessens its solubility in 
water, and may even threaten its existence. The complete de¬ 
composition of the argentic sulphate is only accomplished by a 
long exposure to a high temperature, which is now easily borne 
by most ores and mattes, the easily melted sulphides having been 
converted into almost infusible oxides and basic sulphates. 

Galena (sulphide of lead), when present, is converted almost 
entirely into a sulphate of that metal, which, by a higher tem¬ 
perature, is partially decomposed with the evolution of sulphur¬ 
ous acid and the final production of a mixture of free oxide of 
lead with sulphate, the proportions of these two substances vary¬ 
ing according to the quantity of foreign sulphides present. 

Zinc-blende requires a higher heat for its thorough oxidation 
than any of the preceding sulphides, but with care may be event¬ 
ually changed into an oxide, although a certain amount of basic 
sulphate of zinc nearly always remains. This includes all the 
sulphides assumed to have been present in the ore under con¬ 
sideration, nor will others be encountered in practice unless un¬ 
der very exceptional circumstances. Sulphide of manganese is 
an occasional unimportant constituent of mattes, and presents no 
particular difficulty in calcining, being easily oxidized to a basic 
sulphate, insoluble in water, which is stable except at the highest 
roasting temperatures, when it yields up its acid in the shape of 
S0 2 , and remains as a mixture of manganous and manganic ox¬ 
ides .* 


* This reaction of MnS is given in a small pamphlet devoted to the study 
of the reactions that take place in roasting the Mansfeld copper matte for 
the extraction of silver by the Ziervogel method; but it is impossible to 
credit any individual authorities with the statements made in the preceding 
few paragraphs, they being for the most part matters of general information. 



172 MODERN AMERICAN METHODS OF COPPER SMELTING. 

% 

The gangue-rock of copper ores, being usually siliceous,, 
undergoes no change and exerts no influence upon the 
calcining process, except in so far as it assists in the oxida¬ 
tion of sulphurous to sulphuric acid by contact , as already 
mentioned. 

Calc-spar loses its carbonic acid and is converted into gypsum 
(calcium sulphate), while heavy-spar—sulphate of baryta—under¬ 
goes no change, except in the presence of a powerful reducing at¬ 
mosphere and at a high temperature, when it may be changed into 
sulphide of barium. This is soluble in water, and it has been 
suggested to use its solubility to remove it when its presence is- 
particularly objectionable. A number of trials in this direction 
were made by the author in 1872 on the heavy-spar ores of Mount 
Lincoln, Colorado, with very poor results; as it was found ex¬ 
tremely difficult to reduce the barium sulphate to sulphide with¬ 
out mixing an amount of coal-dust with the ore at least equal to 
the weight of the heavy-spar present—from 30 to 40 per cent.— 
while the BaS formed at this high temperature is only partially 
soluble in water. 

Arsenic and antimony, when present, are usually combined 
with some metallic base, and behave like sulphur to a certain ex¬ 
tent ; but they give off a much smaller proportion as volatile an- 
timonious and arsenious acids, while they combine to a much 
greater extent with the metallic bases, forming salts difficult 
to decompose and extremely injurious to the quality of the 
copper. 

Under such circumstances, the roasting should be continued 
in the usual manner until all the sulphides present are oxidized 
and the resulting sulphates for the most part decomposed. At 
this stage, from 4 to G per cent, of charcoal dust or fine bituminous 
or anthracite coal-screenings should be thrown upon the charge 
and thoroughly incorporated with it by vigorous stirring, the 
heat at the same time being raised to the highest practicable lim¬ 
its. The antimonates and arsenates of iron and copper are rap¬ 
idly reduced by this means, and a considerable proportion of the 
injurious metalloids is volatilized, much to the benefit of the re¬ 
sulting copper. The charge should remain in the furnace until 
all the incorporated carbon is consumed. 

In the foregoing description, the process of calcination lias- 
been carried much farther than is generally needed, or even de- 


THE CHEMISTRY OF THE CALCINING PROCESS. 


173 


sired, in an ordinary oxidizing-roasting as a preliminary to 
fusion. 

Sufficient sulphur must always be present in the smelting 
mixture to prevent the formation of too rich a matte, which en¬ 
tails heavy losses in metal, and other injurious consequences. 
But it is not a simple matter to determine in advance exactly 
the amount of sulphur necessary to produce a matte of any given 
grade. This depends not only upon the character of the furnace 
process to be employed—that is, whether blast or reverberatory 
—but also to a considerable extent upon the manner in which 
the residual sulphur is combined with the bases present; the 
rapidity of the fusion; the quality of the fuel; the volume and 
pressure of the blast; the character of the gangne and flux; 
and numerous other factors. Whatever may be the condition of 
affairs, however, it may be pretty safely predicted that the per¬ 
centage of the resulting matte in copper will almost invariably 
be very considerably lower than is either expected or desired, so 
that there is little danger that the calcining department of any 
newly constructed plant will have too great a capacity in propor¬ 
tion to the rest of the establishment, and many serious errors and 
disappointments can be traced directly to this habit of over-esti¬ 
mating the probable quality of the matte and failing to provide 
sufficient calcining appliances. 

In case of calcination previous to smelting in reverberatories, 
it is well to avoid an excess of air toward the close of the roast¬ 
ing process—a precaution easily effected by closing the working 
openings as far as possible, the rabble passing through a hole in 
the center of a divided door, while the passage of any consider¬ 
able proportion of undecomposed air through the grate is ren¬ 
dered unlikely by the lively fire that belongs to this period. By 
these precautions, the oxidation of any large proportion of the 
iron present to a sesquioxide is prevented, the latter being infu¬ 
sible and unfit to enter the slag until it is reduced to a protoxide. 
This reduction takes place instantaneously in the powerful car¬ 
bonic-oxide atmosphere that prevails in the blast-furnace; but in 
the almost neutral atmosphere of the ordinary reverberatory, the 
sulphur alone plays the part of a reducing agent, and a charge 
composed of the sesquioxide of iron will be found materially to 
delay the process of fusion, besides producing a thick and foul 
scoria. The natural remedy is the admixture of a few per cent. 


174 MODERN AMERICAN METHODS OF COPPER SMELTING. 

of fine coal stirred thoroughly into the mass of the ore, and fired 
on vigorously. 

An examination of the preceding analyses shows what 
a large proportion of the sulphur in the charge will go into 
the matte, especially in the case of rapid smelting in blast¬ 
furnaces. 

Some kind of an idea may be obtained of the probable com¬ 
position of the matte to be produced at any given time by the 
ordinary “ matte fusion assay,” as given in all works on assay¬ 
ing, wherein the ore to be tested is rapidly melted with merely 
enough borax and siliceous flux—say, 100 per cent, of borax and 
an equal amount of pulverized window-glass—to flux its earthy 
constituents, some 10 per cent, of argols or other reducing agents 
being also added. 

But the results are far from satisfactory, and after patiently 
using it for some two years, and being oftener misled than guided 
by its results, I discarded it completely, and trusted principally 
to the eye, occasionally aided by the following calculation, which 
gives better results than any other familiar to me : 

Taking the contents of copper in the charge as a standard for 
comparison, sufficient sulphur should be allotted to it to form a 
subsulphide, the excess of sulphur still remaining being supplied 
with sufficient iron to form a monosulpliide of that metal. If 
other metals are present, such as lead, zinc, or manganese, | of 
the former, h of the second, or ^ of the latter substance may be first 
considered as forming a monosulphide with the sulphur, there be¬ 
ing in such a case just so much less of the metalloid left to take 
up iron. This rule gives quite accurate results in rapid blast¬ 
furnace smelting, and where abundance of iron is present. If 
the rate of smelting be slow, and considerable lime, magnesia, or 
baryta be present, 5 per cent, of the sulphur contents of the charge 
should be deducted before beginning the calculation; and if 
the smelting-furnace is a reverberatory, the resulting matte 
will average 8 per cent, higher in copper than found by this 
formula. 

A simple illustration will make this method of calculation 
more clear. 

We will assume that a roasted ore having the following com¬ 
position is to be smelted in a blast-furnace: 


THE CHEMISTRY OF THE CALCINING PROCESS. 


175 


ANALYSIS OF CALCINED ORE. 


Cu = 9*0 per cent. 
Fe = 45’0 per cent. 
Si0 3 = 27*0 per cent. 
Zn = 2"0 per cent. 


O and loss = 7"2 per cent. 


Pb = 2‘0 per cent. 
S* = 7*8 per cent. 


Total, 100 *00 per cent. 


CALCULATION OF MATTE WHICH SHOULD RESULT FROM FUSION OF THE CAL¬ 
CINED ORE. 

Following the rule given, 


9 Cu require 1*8 S to form a subsulphide. 
f of 2 Pb “ 0*2 S to form a sulphide, 

i of 2 Zn u 0'3 S to form a sulphide. 


This provides for 2'3 per cent, of the 7*8 per cent, of sulphur 
present, leaving 5‘5 per cent., which will take up enough Fe to 
form a monosulphide. Calculation shows that 9'6 per cent, of 
Fe will thus be required, leaving 35'4 per cent, available for the 
slag. 

In order to express the composition of the matte just calcu¬ 
lated, in the ordinary manner, we multiply the amount of each 
ingredient by a common factor that will reduce it to a percentage. 
In this case the factor is 3 - 46. 


9 Cu + 1-8 S = 10*8 x 3-46 = 37-37 per cent. Cu 2 S. 

1*5 Pb- + 0'2 S = 1-7 x 3-46 = 5*88 “ “ PbS. 

1 Zn + 0-3 S = 1-3 x 3-46 = 4*5 “ “ ZnS. 

9-6 Fe + 5-5 S = 15-1 x 3-46 = 52-25 “ “ FeS. 


7"8 per cent. S. 


100*00 per cent. 


Thus the matte from such a charge will contain about 30 per 
cent, copper; the slight loss of sulphur by volatilization and as 
S0 2 being usually fully balanced by the presence in the matte of 
a certain proportion of subsulphides in place of srdphides, or even 
of metallic iron. 

The same charge smelted in a reverberatory furnace would 
yield a matte of nearly 40 per cent. Cu. 

The proper composition of the slag has not been particularly 
considered in this example. It would be somewhat too siliceous for 


* As most of the oxidized compounds of sulphur contained in the cal¬ 
cined ore will be reduced to sulphides in the cupola furnace, it is proper to 
estimate all the sulphur present as metallic sulphur. 






17G MODERN AMERICAN METHODS OF COPPER SMELTING. 

blast-furnace work, requiring the addition of a little limestone \ 
while for reverberatory work, it would be about right as it 
stands. 

From the foregoing statements, it is evident that in ordinary 
copper smelting the calcination of sulphide ores need seldom be 
pushed to the point of perfection indicated when treating of the 
chemical reactions that take place in the roasting. On the con¬ 
trary, a due regard for the proper quality of the resulting matte 
and slag will probably render it advisable to stop the calcining 
process long before the decomposition of the sulphate of copper 
in the charge is complete, and even while a considerable portion 
of undeeomposed sulphides still remains. If, however, the calci¬ 
nation has been carried too far, it is very easy to regulate mat¬ 
ters by the addition to the smelting mixture of a very small pro¬ 
portion of raw sulpliuret ore. 

A glance at the behavior of the various compounds of sul¬ 
phur and bases is essential for the clear understanding of the 
much greater richness of the matte resulting from the fusion of 
any given charge in a reverberatory than in a blast-furnace, and 
of the importance of having a certain proportion of sulphates 
and other oxidized compounds in the smelting mixture, in order 
that they may react on each other in the manner best calculated 
to eliminate the residual sulphur, and thus in a measure make up 
for imperfect roasting. 

In the blast-furnace, but little sulphur can be directly volatil¬ 
ized," and, consequently, simply fuses with the copper or iron pres¬ 
ent to form the artificial sulphide called matte. But the sul¬ 
phates in the presence of carbonic oxide may undergo the follow¬ 
ing reaction: CO + FeO, S0 3 — C0 2 + S0 2 + FeOj the carbonic 
oxide burning to acid, while the sulphuric acid is reduced to sul¬ 
phurous acid, which escapes by volatilization, and the protoxide 
of iron unites with silica to form a slag. But this is true of only 
a very small proportion of the sulphates present, as in the power¬ 
ful reducing atmosphere of the blast-furnace, the sulphurous acid, 
even when once formed, comes in contact with an overwhelming 
proportion of CO, which in burning to C0 2 robs the S0 2 of its 
oxygen, reducing it to sulphur, in which condition it unites with 
iron or copper and enters the matte, thus increasing the amount 
of this product, while it robs the slag of its most valuable constit¬ 
uent. It is interesting to note the striking difference of the re- 


THE CHEMISTRY OF THE CALCINING PROCESS. 


177 


action in the reverberatory furnace, where the atmosphere may 
be regarded as neutral; CO, the most powerful reducing agent, 
being virtually wanting: 

Cu 2 S + 4 CuO,S0 3 = 6 CuO + 5 S0 2 . 

Cu 2 S + 2 CuO,S0 3 = 2 Cu 2 0 + 3 S0 2 . 

Cu 2 S + 2 Cu 2 0 = 6 Cu +’ S0 2 . 

By studying these formula?—taken from Percy, Kerl, and 
Rivot—it will no longer seem strange that the reverberatory pro¬ 
duces so much richer matte than the blast-furnace from the same 
charge. Nearly all the reactions between sulphides and sul¬ 
phates result in the formation of oxides and volatile S0 2 , and 
were it not for an almost invariable preponderance of undecom¬ 
posed sulphides in the charge, the elimination of the sulphur 
might theoretically be almost complete. It is by this all-impor¬ 
tant but frequently neglected establishment of a proper proportion 
between the sulphides and sulphates, that extraordinary results 
may be obtained in reverberatory smelting, and the roasting 
plant greatly reduced. 

Although treating of smelting, this matter belongs strictly, to 
the calcining department, and presents a field for study of great 
interest and practical value. A close analogy may be found in 
the various reverberatory processes as applied to the smelting of 
galena ores, where almost exactly the same results are produced, 
using lead instead of copper, and obtaining metallic lead with a 
minimum amount of calcination, and putting to accurate prac¬ 
tical use the reactions just explained, although text-books on 
copper metallurgy are strangely silent on this important subject. 

The length of time requisite to roast a charge of ore of a 
given weight in the long furnace under discussion depends, of 
course, upon the composition of the charge and the degree of 
thoroughness in oxidation desired. Each of the four hearths of 
this furnace has an effective area of about 250 square feet, and 
can consequently receive 4,000 pounds of ore if only 16 pounds 
to the square foot are charged. This is a very moderate charge, 
especially for heavy sulphide ores, but will ordinarily give better 
results than a heavier burden. It will cover the hearth about 
2J inches deep when charged, increasing in bulk to about 4 
inches at the completion of the process. By shifting each charge 
every four hours, the ore will remain 16 hours in the furnace, a 


178 MODERN AMERICAN METHODS OF COPPER SMELTING. 

time generally ample to produce the desired effect. On this 
basis, the furnace would put through 12 tons in twenty-four 
hours, which may possibly be increased to 1G tons by substitut¬ 
ing three-hour drops for the four hours recommended. But this 
is the extreme limit for two men per shift, nor will these figures 
be reached under ordinary circumstances. Two cords of wood 
or 2,240 pounds of soft coal should supply the grate for twenty- 
four hours, the supply of air to the ash-pit being kept at the low¬ 
est possible point. The sulphur contents of the ore furnish a 
much greater proportion of the heat than does the fuel on the 
grate. 

The manipulations pertaining to the ordinary calcination of 
ore are too simple and generally known to be worthy of a place 
in a condensed treatise. 

The following experiments form part of a series extending 
over some ten years, which it was at one time hoped to amplify 
and carry out into something of positive value. But increasing 
professional cares, and the impossibility of having the numerous 
analyses made that constitute an essential part of the work, have 
prevented the fulfillment of this hope. The material collected 
’will, however, be used wherever it may prove of value in the 
course of this treatise. The author desires to acknowledge the 
assistance of Messrs. J. F. Talbot and F. Ames, and others, in 
the chemical portion of the work. 





Dry weight 
ol charge. 


Copper in roasted 

ore. 

Sulphur in 
roasted ore. 


No. of 

sample 

Copper. 

Sulphur, 

Weight 

lost. 

As ox¬ 
ide. 

's £ 

Ol c3 

As sul¬ 
phide. 

Total. 

si 

og 

HM ^ 

1 ... 

Pr ct. 
7'6 

Pr ct. 
370 

Lbs. 

4,130 

Pr ct. 
14-5 

365 

3 25 

1-65 

8-55 

6*41 

16 

2... 

7'6 

39 0 

4,130 

11-3 

2-27 

3-10 

280 

8-17 

11-30 

12 

3... 

16-4 

31 0 

3,925 

6-4 

7-10 

344 

6-80 

17-34 

8-20 

18 

4... 

16 4 

310 

3,940 

95 

12-80 

2-80 

210 

17 70 

4-60 

24 

5... 

38'8 

243 

3.610 

62 

29-20 

440 

370 

37-30 


18 

6... 

62-2 

22'0 

3,580 

37 

54 "CO 

380 

6-60 

64-30 


18 

7... 

CO 

s 

2P4 

3,800 

24 

61 60 

5 "40 

7-90 

74-90 


18 


Remabks. 


Heavy pyritous ore. 
Same ore. 

I Purple ore with 
< much pyrites and 
f some zinc-blende. 
Same ore. 

Matte from cupola. 

J Blue metal from 
j reverberatory, 
j White metal from 
1 reverberatory. 


The loss of weight from the removal of the sulphur is 
partially balanced by the oxygen combining with the metallic 
bases, and is exceedingly variable, as may be seen by this table. 
The loss in copper during calcination is very small, and al- 

































THE CHEMISTRY OF THE CALCINING PROCESS. 


179 


most entirely mechanical, being for the most part recoverable 
where proper arrangements are made for the deposition of the 
flue-dust. Average results from personal experience show a loss 
of about 1J per cent, of the original copper contents of the ore 
during calcination. 

This flue-dust is usually of very much lower grade than the 
ore from which it results, being diluted with the dust from the 
fluxes, fuel, etc., and generally contains from 20 to 30 per cent, 
of its value in a soluble form, thus prohibiting the use of water 
as an aid to its condensation, unless provision is made to precipi¬ 
tate the dissolved metal. 

Unless the ores treated are of remarkable purity, it is best to 
smelt the flue-dust by itself, making it into balls with clay or 
lime and adding the necessary fluxes. Otherwise, the quality of 
the metal is likely to suffer, as the substances most injurious to 
it—arsenic, antimony, and tellurium—are volatile, and sure to be 
condensed in the flues, thus being collected in a concentrated 
form. 

COST OF CALCINING. 

The running expenses of a calciner, aside from the slight re¬ 
pairs just alluded to, are small and regular. In twenty-four 
hours, it will burn one ton of soft coal (2,240 pounds) at $5, or 
2 cords of pine wood, and require the services of four men at $2, 
and one-quarter the time of a laborer to weigh and bring the 
charges to the hoppers, the furnace-men dumping and drawing 
their own charges. This amounts to— 


Coal, 1 ton.$5.00 

4 furnace-men at $2. 8.00 

i weigher at $2.50 

Wear and repairs on tools, car, etc.30 

Oil, lights, and miscellaneous,.80 


Proportion of superintendence (say one foreman to eight furnaces). .50 


Total 


$15.10 


Considering that twelve tons per day of highly sulplmreted 
ores can be quite thoroughly calcined in such an apparatus, it 
shows a cost of about $1.25 per ton of ore, which leaves but little 
opportunity for the inventors of automatic roasting-furnaces to 
cheapen the results that can be obtained in the old-fashioned cal¬ 
ciner, when built of proper dimensions and provided with a pow- 









180 MODERN AMERICAN METHODS OF COPPER SMELTING. 


erful draught. The above figures have been repeatedly obtained 
by the author (reduced, of course, to current prices), and after a 
tolerably extended metallurgical experience and a trial of almost 
■every reasonable type of roasting apparatus, he still emphatically 
recommends the simple and well-known open-hearth reverbera¬ 
tory calciner for the preliminary roasting of copper ores and 
mattes* 

The consumption of fuel depends largely upon the fireman. 
It is as easy for him to burn two tons of coal as one j but in a 
properly constructed furnace, with a moderately favorable ore 
carrying 20 per cent, or more of sulphur, the quantity above in¬ 
dicated will suffice perfectly. 


* See latest results of roasting in Bruckner’s cylinders. 



CHAPTER IX. 


THE SMELTING OF COPPER. 

By this term, we understand the fusion of the copper-hearing 
material and of whatever fluxes may be necessary, when the cop¬ 
per, owing to its higher specific gravity, separates from the slag, 
and is recovered by appropriate means. In the case of oxidized 
ores, it is obtained at once in a metallic condition, somewhat 
adulterated with sulphur, iron, and other foreign substances, but 
requiring only a single operation, or, at the outside, two more 
operations, to bring it into merchantable form. 

But when it occurs in combination with sulphur or arsenic, 
and accompanied with an excess of foreign sulphides, the result 
of the first fusion is merely a concentrated ore, freed from the 
earthy gangue, and resulting from a combination of the copper 
with sufficient of the sulphur present to form a subsulphide, to 
which is added as much monosulphide of iron as corresponds to 
the remaining sulphur, always excepting such portion of that 
metalloid as is volatilized during the process of fusion. If tin, 
zinc, lead, silver, antimony, or arsenic are present, they combine 
with the sulphur for the most part and enter the matte, their 
affinity to sulphur being in the order mentioned, according to 
Fournet’s experiments. 

These various sulphides unite either physically or chemically 
to form the substance technically known as matte, or metal, or 
regulus, the latter term not to be confounded with the term 
regule, which belongs to a matte of a certain richness in copper, 
and possessing peculiar and well-marked characteristics. 

From the above statements, it is plain that, other things be¬ 
ing equal, the grade of the matte depends on the amount of sul¬ 
phur in the ore. 

It might, at first glance, seem more economical to push the 
roasting process to the extent of removing all the sulphur, thus 
bringing about the same conditions that prevail in the smelting 


182 MODERN AMERICAN METHODS OF COPPER SMELTING. 

of an oxidized ore; but practice has shown the futility of such a 
scheme, as, aside from the great expense and difficulty of effect¬ 
ing such a complete calcination, the resulting slags are always 
too rich in copper; and the copper when produced cannot 
compare in quality with the metal resulting from the ordinary 
methods of treatment, where the numerous alternate oxidizing 
and reducing influences remove, for the greater part, those 
traces of impurities that are almost invariably present, even in 
the purest ores, and which have such a powerful effect on the 
physical condition of the finished metal. 

Copper smelting, therefore, is naturally separated into two 
great divisions, according to the composition of the material to 
be treated: 1. Smelting of ores containing sulphur (arsenic, anti¬ 
mony). 2. Smelting of ores free from sulphur (etc.). But each 
of these classes may be again divided, according to the apparatus 
employed, into— 

A. Smelting in blast-furnaces. 

B. Smelting in reverberatory furnaces. 

But few exact statements have been published by practical 
metallurgists of comparative results obtained by running the two 
classes of furnaces side by side on the same ore, and under the 
same management and conditions. The fact that, during the 
author’s career as manager of various copper works, he has 
smelted about an equal amount of ore in each class of furnace, 
and in several instances carried out quite extensive comparative 
tests at the same works as to cost, capacity, etc., may lend value 
to such statements. 

Considerable animosity has been evinced by the partisans of 
the reverberatory and of the blast-furnace system of treatment— 
or Swansea and German methods, as they are often termed. 

Much of this arises from a want of exact knowledge and ap¬ 
preciation of the advantages and peculiarities of the opposing 
systems. 

Since blast-furnace smelting has obtained a footing in the 
United States, it has become so changed from its original as to 
be scarcely recognizable, and as here used, by the more advanced 
metallurgists, can challenge competition with the reverberatory 
under most circumstances, and, where the conditions are at all 
favorable, can show results far surpassing the best Swansea work 
in yield, economy, and capacity. 


THE SMELTING OF COPPER. 


183 


That this may seem novel or even doubtful to English smelt¬ 
ers, is quite natural, when it is recollected that the full extent of 
these remarkable advances is known to comparatively few metal¬ 
lurgists, and that very little relating to the same has been pub¬ 
lished. 

It is with the modern American form of the German copper 
process that all comparisons must be instituted; and this com¬ 
prises not only a great improvement in the processes of calcina¬ 
tion and the construction and management of the blast-furnaces 
used, but, in many cases, the employment of reverberatories for 
certain portions of the matte concentration, while the process of 
refining is in nearly all cases carried on according to the 
Swansea method. 

In any attempt at a comparison of these two great methods 
of smelting, one is confronted by the inextricable mingling of 
the commercial with the metallurgical that is so characteristic of 
the English system. Without a thorough understanding of the 
peculiar local conditions under which the ores are purchased at 
the Swansea ticketings, it is impossible to fully appreciate the 
fine points of the complex and ingenious system that time and 
circumstances have elaborated, or to realize the important influ¬ 
ence exercised on the whole subsequent series of operations by 
the amount of judgment displayed in the purchase of the ores, 
and in the adaptation of the same to the immediate needs of the 
works.* The Swansea smelter receives his ore in numberless 
small parcels, differing not only in richness, but in purity and 
other qualities. To carry out the reverberatory process to the 
best advantage, he requires, in addition to the main supply of 
sulphide ores, a certain proportion of oxides and carbonates, all 
of which are obtainable in the public ore market. His coal is of 
the cheapest and most suitable quality, and the refractory mate¬ 
rial—fire-brick, clay, siliceous sand, etc.—is obtainable at prices 
far below American rates. He also has at his command a body 
of experienced and skillful workmen who have grown up at the 
furnaces, and who, at very low wages, are fully capable of exe¬ 
cuting all the difficult operations demanded by this system of 
treatment. In addition, he has a market for his product, where 
every variety of metal brings the highest justifiable price. 

* See Percy on Copper, for a full description of the Swansea ore sales, 
together with quality and value of ore offered. 




184 MODERN AMERICAN METHODS OF COPPER SMELTING. 

It is very evident that such a state of affairs cannot he com¬ 
pared with average American conditions, where, in the greater % 
number of instances, the ore supply comes from only one or two 
sources, constant in its composition, and usually in very large 
quantities. This, with the high wages and exceedingly expensive 
fuel, has caused the introduction of labor-saving machinery and 
appliances to an unprecedented extent, as well as a constant en¬ 
deavor to lessen the proportion of fuel to ore smelted. The lack 
of steady and skilled furnace-men, and the high cost of refractory 
materials, have also had a powerful influence in shaping the proc¬ 
esses of treatment, and have perfected the water-jacketed cupola, 
without which many of our most successful metallurgical enter¬ 
prises could hardly exist. The same influences have concentrated 
the works for the refining of copper in a very few hands, and 
located them with the view to cheap coal and refractory materials 
and to a market for the finished product. Another factor that 
has had its effect in greatly simplifying our domestic process of 
refining is the extreme purity of the lake copper, which, in this 
country, takes the place of the higher grades of English copper, 
there produced by special refining processes, and commands cor¬ 
respondingly higher prices. 

BLAST-FURNACE SMELTING. 

a. Of sulphide ores. 

b. Of ores free from sulphur. 

(I .—TREATMENT OF SULPHIDE ORES. 

The fusion of sulphide ores in blast-furnaces may take place 
either with or without a previous calcination, as has been already 
referred to. 

Where the percentage of sulphur is small in proportion to the 
copper contents, a sufficiently high-grade matte may be obtained 
by the direct fusion of the raw ore, with the addition, of course, 
of the proper quantity of basic substances, such as iron ore, lime¬ 
stone, etc., to flux the very large proportion of gangue rock, 
which, in most cases, consists of quartz or some highly siliceous 
substance. As the amount of basic material required to flux 
silica is very large, about two pounds to one of silica, highly sili¬ 
ceous ores can be remuneratively smelted only under exception¬ 
ally favorable circumstances. Otherwise, such ores would often 


THE SMELTING OF COPPER, 


185 


be more advantageously treated by one of the wet processes. No 
better flux for silica can lie had than the ferruginous slag arising 
from the concentration-smelting of copper mattes, which usually 
contains about one per cent, of copper, but can seldom be ob¬ 
tained in such quantities as to form a permanent flux for any 
considerable amount of highly siliceous ore. 

The class of copper ore most commonly subjected to blast¬ 
furnace treatment in the Eastern portion of this country is a 
highly pyritous material, usually having from 2 to 6 per cent, of 
copper, and varying amounts of silica. This is first burned for 
the manufacture of sulphuric acid, after which the cinders are 
smelted for copper. The ores from Capelton, Province of Que¬ 
bec ; Milan, New Hampshire; Virginia; and Georgia carry an 
excess of iron, and to them may be added the monosulphide 
ores found at Ely and Copperas Hill, Vermont; Ducktown, 
Tenn.; and Ore Knob, North Carolina. In the West, a large 
number of mines furnish copper ores usually of somewhat greater 
richness, but in which the silica is in excess, rendering the smelt¬ 
ing more difficult and occasionally making the employment of 
reverberatory furnaces advisable. To this class belong, also, the 
ores of the Douglas and many other Maine deposits; the St. 
Genevieve, Mo., mines; a large class of argentiferous copper 
mines in San Juan District, Colorado; most of the Butte City 
veins; and a series of important though little known deposits in 
Lower California and Nevada. This brief enumeration includes 
most of the types of sulphide ore likely to come to the blast¬ 
furnace ; and the first object of the metallurgist is to see how he 
can form a proper slag at the least possible cost. 

A proper slag for a blast-furnace should contain between 24 
and 36 per cent, of silica, although, under pressure of circum¬ 
stances, these extreme figures may be either raised or lowered 
about 6 per cent, without seriously compromising the running of 
the furnace. But every per cent, of silica in excess of 36 will be 
felt in a rapid reduction of the amount smelted in twenty-four 
hours. 

As it is usually a long time before the young metallurgist 
fully appreciates the enormous damage that even a slight excess 
of silica will effect, the writer desires particularly to emphasize 
this point, and to declare that, according to his own experience, 
three-fourths of the troubles and annoyances experienced by the 


186 MODERN AMERICAN METHODS OF COPPER SMELTING. 


blast-furnace manager result from this cause. There are many 
instances of furnaces that have given trouble from the day of 
their first starting, being relieved by a slight addition of iron ore, 
and smelting operations have changed from a loss to a profit, 
capacity being increased 40 per cent., and the campaign length¬ 
ened from 20 days to several months by slightly increasing the 
insufficient charge of limestone and iron. 

In speaking of modern blast-furnace smelting, we may well 
omit any lengthy description of the small brick furnaces so 
familiar to all who look over the illustrations in Kerl and Platt- 
ner. The economy of larger furnaces has been thoroughly dem¬ 
onstrated, and in the present treatise, plans and descriptions will be 
mostly confined to the two principal types of furnace now in use: 

1. The water-jacket furnace, with its various modifications. 

2. The long rectangular brick furnace. 

With a thorough understanding of the construction and man¬ 
agement of these two varieties of furnace, the metallurgist is 
amply prepared to obtain the best results known to modern en¬ 
gineers. 

1. The water-jacket furnace, with its various modifications. 

Without attempting to determine to whom the credit belongs 
of adapting the principle of water-cooling to copper blast¬ 
furnaces, it may be hailed as the greatest advance in the treat¬ 
ment of that metal that has been made since the introduction of 
the English method of refining on the hearth of a reverberatory 
furnace. With its employment, the burning out, and consequent 
u freezing up,” of the furnace from the half-fused masses of molten 
fire-brick, have become things of the past, and campaigns have 
been extended to an unprecedented length. In fact, where no 
accident occurs, nothing compels the stoppage of the furnace ex¬ 
cepting the need of general repairs to machinery, etc.; the cleans¬ 
ing of the interior of the jacket from sediment; and the possible 
choking up of the furnace shaft with accretions of sulphides of 
zinc or lead, which occur in minute proportions in almost all cop¬ 
per ores. 

The material of which the jacket is composed may consist of 
cast-iron, wrought-iron, or mild steel. The brand of wrouglit- 
iron known as fire-box iron is preferred by the author, as less 
liable to scale and blister by the heat, and because capable of be¬ 
ing bent without weakening. Where cast-iron is used, the fur- 


THE SMELTING OF COPPER. 


187 


naee is composed of several sections, held together by clamps or 
rings; but aside from the excessive weight, this material is some¬ 
what liable to crack when exposed to extreme fluctuations of 
temperature, although, as of late the castings are made from five- 
eighths to three-quarters of an inch thick, with a water-space of 
from four to ten inches, this accident is much less likely to occur. 
The thickness of the wrought jackets need not exceed that of or¬ 
dinary boiler plate, and this material is peculiarly suited to cir¬ 
cular furnaces, the inner plate having been found to buckle and 
weaken, owing to difference of expansion, when used in long rec¬ 
tangular furnaces—an observation made by Mr. J. B. S. Her- 
reshoff, of New York, and which he has obviated by using a very 
elongated oval shape in place of the rectangular. 

Although the circular form possesses certain advantages for 
smelting-furnaces, experience has taught us that the ordinary 
blast used in copper smelting, which seldom exceeds three- 
quarters of a pound per square inch, cannot well penetrate to the 
center of a charge in a furnace of greater diameter than fifty 
inches, this being the outside limit in cases where at least' one- 
lialf the charge is in lump form. In wrought-iron jackets, the 
width of the water-space has been diminished little by little, until 
even two inches has become a not uncommon standard, and its 
reduction over several square feet of surface to one and one- 
quarter inches has not been accompanied with any evil results. 
The cold feed-water is generally introduced near the middle or 
lower portion of the jacket, and doubtless settles to the lower 
point at once, rising gradually as it becomes heated, and escaping 
through a pipe of somewhat greater area from the upper portion 
of the jacket. It is best to have the escape-pipe tapped into the 
water-space in such a way that it is even with the extreme upper 
surface, thus preventing the accumulation of any steam that 
might form. Circulating pipes are introduced into the water- 
space by some of the best manufacturers; but while not prepared 
to deny their value, the author has run water-jacketed furnaces 
of many sizes and shapes, and under varying conditions, and has 
never felt the need of any guide-plates, the difference in tempera¬ 
ture of the incoming and outgoing water always being sufficient 
to keep up a lively circulation to the most distant point, while 
any sediment introduced in the water could always be easily re¬ 
moved through the hand-holes provided for that purpose. 


188 MODERN AMERICAN METHODS OF COPPER SMELTING. 


The following figures, deduced from personal experience, give 
furnaces of this description, and of various diameters, and the 
quantity of water required when in full blast: 


Water per hour while Water per hour during 

Diameter. blowing in and out. normal running. 

Inches. Galls. Galls. 

24. 900. 460 

30.1,200. 600 

36.1,450. 950 

42.2,200.1,200 

48. 3,000.1,500 

These figures refer to a supply of fresh water; but where the 
same water is used over and over again, about 3,000 gallons per 
twenty-four hours are required to make up the loss by evapora¬ 
tion, etc., in a 36-inch furnace in the dry, hot climate of Arizona. 
Prof. F. L. Bartlett has arranged a tank at such a height that its 
upper surface is a trifle higher than the water level in the jacket, 
by which means a constant circulation takes place, requiring only 
the addition of sufficient fresh water to replace the evaporation. 
This may require a little extraneous aid from a force-pump or 
steam-jet during the period of blowing in ; but in a few hours, 
when the upper portion of the furnace is cooled down to its 
normal condition, this arrangement is said to answer every pur¬ 
pose, though the water may from time to time become a little 
hot, and even form a certain amount of steam. To save all cal¬ 
culation, it may be stated that a 2^-inch feed-pipe, with a 2f-inch 
discharge-pipe, the former coming from a tank that will give eight 
or ten feet pressure, will give all the water necessary for a 42- 
inch furnace. 

Where the hot discharge-water is not used over again, it is 
economical to employ it for the boiler, or in winter to lead it into 
some lower tank, or where it may be used for ore-concentration 
purposes, if such a plant is present. The furnace-jacket should 
always be provided with a drain-cock to empty it when not in 
blast in cold weather. 

While the weight and clumsiness of cast jackets prevent their 
being made of any great size, so that the first jackets only occu¬ 
pied a narrow circular ring at the level of the tuyeres and for a 
few inches above, it has now become quite customary to cast 
them in sections of from 30 to 60 inches in height, while the cir- 












THE SMELTING OF COPPER. 


189 


cular or oval wrought jackets usually extend from a point some 
10 inches below the tuyeres, to the threshold of the cliarging- 
door, a distance of from 6 to 10 feet. This saves all brick-work, 
excepting the small amount in the bottom, and the flue on top, 
by which the gases are conducted to the stack. This flue and 
upper brick-work are usually supported on light iron columns, 
the jacket itself being either suspended from the same columns 
by a ring, or resting on cast legs of its own. 

The bottom of the furnace may be constructed in various 
ways ; but in the smelting of roasted pyritic sulphide ores, Amer¬ 
ican practice is pretty unanimous in entirely doing away with 
the ordinary deep crucible, substituting for it merely a sloping 
bottom a foot or less below the tuyeres, from which the entire 
molten material escapes through a narrow groove under the 
breast, then first entering an outside crucible or u well/’ in which 
the matte separates from the slag, and is tapped into molds, 
while the slag flows from a spout into iron pots arranged on 
wheels for convenient dumping. It is this transfer of the 
crucible from the inside to the outside of the furnace that has 
divested cupola work of most of its terrors. By this simple 
means, we escape the troublesome chilling over of the metal in 
the crucible, and the frequent freezing up of the tap-hole, render¬ 
ing it impossible to empty the furnace without the most labori¬ 
ous and tedious work. The formation of sows and other kindred 
products is also prevented by the immediate escape of the fused 
ore from the powerful reducing action of the fuel, as are also the 
cutting down of the crucible and thinning of its surrounding 
walls until the metal and slag burst through, and a long list of 
lesser troubles, familiar to every practical furnace-man. 

The advantages gained by modern blast-furnace practice may 
be partially estimated by comparing the following statement 
with the results given in succeeding pages of this treatise. 

As a matter of historical interest, it may be put on record 
that the first “ well ” used in connection with a copper furnace in 
this country was built by James Douglas, Jr., at his Plioenixville 
works, in 1879. The author is unable to find any authentic in¬ 
formation of any earlier use of the modern form of well, or inde¬ 
pendent fore-hearth. 

In a valuable and interesting lecture delivered by Mr. Henry 
Hussey Vivian, M.P., at Swansea, December 20th, 1880, on the 


190 MODERN AMERICAN METHODS OF COPPER SMELTING. 


history and processes of copper smelting,* after admitting that 
the blast-furnace invariably excels all other apparatus in the pro¬ 
duction of a clean slag (that is, free from metal), he adds : “It 
has a constant tendency to reduce the oxide of iron contained 
in the calcined ore into metallic iron, and thus to produce a mass 
of infusible material at the bottom of the furnace, which, in no 
long period, causes the entire or partial destruction of the fur¬ 
nace. Even in the best managed continental works, I have 
proofs that the so-called iron 1 sows 7 are produced; in fact, they 
are an almost unavoidable incident of melting calcined copper 
ores in blast-furnaces. 77 And in referring to his personal exam¬ 
ination of the ancient slag-piles surrounding the famous Rio 
Tinto and Tharsis mines, in Spain, he says: u I examined crit¬ 
ically the slag-heaps, and was astonished at the freedom of the 
slags, made, perhaps, two thousand years ago, from prills. At 
this moment, with all my accumulated experience of copper smelt¬ 
ing, I don’t know how they made those heavy irony slags so 
clean. 77 

If Mr. Vivian had had the use of the blast-furnace forced 
upon him under these conditions, there is little doubt that he 
would have solved this problem that now perplexes him. At any 
rate, the Americans have solved it in the most satisfactory man¬ 
ner, and can refer the inquirer to the records and practice of 
almost any of the principal copper-works in this country, where 
slags of the most highly ferruginous character, as well as the 
most siliceous, are produced in blast-furnaces, not only free from 
prills, and without the slightest accompaniment of iron sows, 
but also far lower in chemically combined copper than can pos¬ 
sibly be made in reverberatories. How such results are obtained, 
will be explained when treating of furnace management, although 
the improved construction has also an important influence in 
effecting these results. 

In the treatment of sulphide ores, the practice, formerly com- 


* Copper Smelting : its History and Processes. By Henry Hussey Vivian, 
M.P. A Lecture delivered at Swansea, in the Theatre of the Royal Institu¬ 
tion of South Wales, December 20th, 1880. To which is added : A History 
of the Baltimore Copper Works at Canton, Maryland; Sketches of the For¬ 
est Copper Works, and the Hafod Copper Works, Swansea, South Wales. 
With illustrations. New York : The Scientific Publishing Company, 27 Park 
Place. 1881. 8vo, pamphlet. 



THE SMELTING OF COPPER. 


191 


mon, of having the crucible wholly or in part under the main 
body of the furnace—as in the German Tiegel-Ofen and Sumpf- 
Ofen—can under no conditions be recommended. Those inter¬ 
ested in this system of furnace construction will find full details 
regarding the same in any of the standard German works on the 
subject, and in the section of this treatise devoted to brick fur¬ 
naces. 

The bottom of the furnace, according to modern practice, is 
brought up to within from G to 12 inches of the tuyere level, in 
most cases sloping slightly toward the breast, so that the entire 
molten contents may flow out through a narrow channel under 
the latter, and discharge into an anterior compartment, consist¬ 
ing either of a deep basin formed of “steep” ( Gestiibbe , Brasque ), 
or a large rectangular box, made of fire-brick held together by 
iron plates, and in which the separation of matte from slag takes 
place quietly and thoroughly. 

Provision is made to prevent any escape of blast under the 
breast, either by so thoroughly covering over the orifice and 
channel that only a minute groove exists, which is constantly 
filled to its utmost capacity with the molten ore, which soon 
forms an impervious cover to its channel; or by so raising the 
terminal slag-spout, and lowering the anterior wall of the fur¬ 
nace, that the blast is securely “ trapped,” just as sewer gas is 
prevented from escaping in an ordinary drain. 

The first method, combined with the steep crucible, is best 
adapted to the production of pig-copper or very rich metal, as in 
matte concentration, owing to the great tendency to chill of these 
substances; while the latter plan is far preferable for ordinary 
ore-smelting, where matte of much lower grade is produced in 
considerable quantities. Where pig-copper is produced on a large 
scale, and in furnaces of considerable capacity, it is best to drop 
the “ steep ” crucible entirely, as the large volume of hot metal 
will permit the use of the much preferable brick “ well ” without 
chilling. In either case, the furnace should be taken in hand by 
the head smelter as soon as the water-jacketed shell is properly 
suspended in position with its upper brick-work complete, and 
the connection established between the same and the stack that 
is to convey away its gases. 

If the furnace is to be used for matte concentration or for the 
production of pig-copper from roasted matte, and consequently 


192 MODERN AMERICAN METHODS OF COPPER SMELTING. 

provided with a steep crucible, four iron plates should be pro¬ 
vided, forming* a rectangular box about 3J feet high, some 4 
inches wider than the furnace on each side, and extending from 
the back to 36 inches in front of the breast. The front plate is 
provided with the usual cast-iron slag-spout, fitted with a groove 
to slip on without bolts, while one side plate should be perforated 
with a small hole or, better, slit, two inches wide and seven inches 
high. As this is the tap-hole, its lowest point should correspond 
with the apex of the inverted cone-shaped crucible.* 

A heavy matte-spout, eight inches long, and at least two 
inches thick on the bottom, and cast as part of a strong square 
plate, should be bolted on at the lower edge of the opening, an 
arrangement found necessary for the proper and efficient plug¬ 
ging of the tap-hole. A foundation for this iron box, which is 
held together by bolts through ears or other simple means, should 
be made by either laying down thick iron plates of the proper 
dimensions, or by putting in a tight floor of fire-brick on end, 
laid in thin clay mortar with an addition of 10 per cent, of sili¬ 
cate of soda. This will prevent the gradual penetration of matte 
into the rock foundation, and is a necessary precaution. Upon 
this the portion of the rectangle corresponding to the base of the 
furnace is built up as a solid column of fire-brick to within 10 or 
12 inches of the tuyeres. 

In some furnaces, the water-jacket is continued for a consid¬ 
erable distance below the tuyeres. In any case it is proper to 
continue the brick-work, on the outside at least, to the edge of 
the jacket, surrounding the lower portion of the latter with a few 
courses, to insure a tight joint. 

In the anterior half of the Aon fore-hearth, a single row—4J 
inches—of fire-brick is sufficient on the sides, while a 9-inch wall 
is usually built in front, an elongated opening corresponding to 
the tap-hole being left in the brick-work. 

It is now evident that the fore-hearth is filled in its posterior 
half with a solid mass of brick-work, extending up to, and be¬ 
coming continuous with, the circular shell of the furnace proper* 
while the anterior half contains a large square opening, sur- 


* The cuts accompanying the description of the Herreshoff and Orford 
furnaces may "be referred to in connection with this and succeeding para¬ 
graphs. 





THE SMELTING OF COPPER. 


193 


rounded by a brick wall, extending down nearly to the founda¬ 
tion of the structure; communicating by a channel under the 
breast with the interior of the furnace; opening into the tap-hole 
on one side, and into the slag-spout in its upper anterior wall. 

The interior of the furnace is now provided with a bottom,, 
consisting of four parts ground calcined quartz to one part plastic 
fire-clay. This is firmly tamped upon the brick base and carried 
in a wedge-shaped wall around the sides of the circular interior, 
resting against the water-jacket, and thinning out to nothing just 
below the tuyere openings. The component parts of this mixt¬ 
ure should be ground through a 16-mesh screen, or finer, and 
after a thorough mixing, should be slightly moistened, and 
tamped firmly into place with iron bars, shaped on the end like 
a four-leafed clover, and slightly heated, to prevent adhesion of 
the material. 

A layer of three or four inches is quite sufficient for an or¬ 
dinary furnace bottom, it being only necessary to protect the 
brick-work until there is deposited from the smelting charge an 
exceedingly refractory mixture of metallic iron, matte, and slag, 
which forms a massive and permanent bottom, far superior to 
any artificial substance. It is only in smelting very poor pyritous 
ores, producing a large quantity of low-grade matte, that any 
“ cutting down ” of the bottom occurs. The measures appropri¬ 
ate to this condition of things will be discussed when treating of 
the large brick furnaces, in which this class of material is com¬ 
monly produced. 

The furnace bottom should slope slightly toward the breast, 
at which point it meets the “ steep ” (German, Gestiibbe ; French, 
Brasque) with which the anterior compartment is filled, and in 
which the crucible is formed, its deepest point communicating 
with the tap-hole in the side plate. 

This moderate and economical use of steep must not be con¬ 
founded with the old-fashioned practice of establishing an enor¬ 
mous fore-hearth, filled with this material, and requiring constant 
repairs and attention. Although abolished in many modern 
works, it possesses peculiar qualities, which render it very valu¬ 
able in certain blast-furnace operations—such as the smelting of 
calcined matte—where the product is either pig-copper or a very 
high-grade matte, and the capacity of the furnace not large. 

Both of these substances have a strong tendency to chill, 


194 MODERN AMERICAN METHODS OF COPPER SMELTING. 

especially when using the exterior crucible, which is for the most 
part prevented by the use of steep, which, besides being an ex¬ 
cellent non-conductor, seems actually to generate heat—possibly 
from the slow combustion of its carbon—thus preserving the 
metal fluid, while any chill that may form in the crucible is easily 
removed without damaging its walls and interior, as would be 
the case with clay or brick-work. 

The permanency of the basin and tap-hole depends greatly 
upon the quality of the steep, which should be made as follows : 
Crush the constituents separately through a 20-mesli screen, or 
as much finer as is practicable. A Bogardus or Sturtevant mill 
will be found useful for this purpose, and has a much greater 
capacity than the light stamps often used. Mix very thoroughly 
while dry, and moisten with water through a rose nozzle to such 
a degree that the mass will ball when pressed vigorously in the 
hand, without imparting any dampness to the skin. Tamp firmly 
with inch square bars, and avoid stratification by adding a shovel¬ 
ful at frequent intervals, and before a hard surface is produced 
by the pounding. The following proportions are suitable for 
varying conditions. When the product is metallic copper, use 
by measure: 3 parts coke, 2 parts raw fire-clay; or 4 parts coke, 
2 parts raw clay, 1 part burnt clay or ground brick; or 3 parts 
charcoal-dust, 2 parts raw clay, 1 part ground red brick. For a 
product of rich matte, use: 7 parts coke, 5 parts raw clay; or 3 
parts charcoal, 2 parts raw clay, 1 part burnt red brick. 

A large proportion of carbon counteracts the chilling of the 
metal and the consequent formation of skulls in the fore-heartli, 
but is less able to stand mechanical violence than the heavier 
steep, which has more plasticity. Charcoal-dust makes a some¬ 
what fragile mixture, but an excellent one for retaining heat. 

The arrangement just described is particularly suited to a 
small slow-running furnace, where it is intended to make a rich 
product, and where reasons exist for producing a slag sufficiently 
free from copper to be at once rejected. That this is perfectly 
practicable is demonstrated at various establishments in this 
country, where, by a somewhat lavish expenditure of fuel, a light 
, a very slo\^ run, a slag containing below 0*7 per cent, 
of copper and exceedingly ferruginous is produced in conjunction 
with pig-copper. The material smelted is stall-roasted matte, 
with a very small addition of old brick and furnace ends, and in 


THE SMELTING OF COPPER. 


195 


spite of the character of the charge and the powerful reducing 
action due to the slow run, the formation of all metallic iron is 
avoided a result almost impossible to obtain in furnaces with 
an interior crucible.* 

To prevent the delay arising from the frequent though slight 
repairs indispensable from this form of furnace, it is sometimes 
customary to widen the fore-hearth sufficiently to contain two 
crucibles side by side and used alternately. 

The copper may be removed from the crucible either by tap¬ 
ping into molds of sand or iron, or by ladling, the latter method 
being more frequently employed where the product is pig-copper, 
owing to the difficulty of opening the tap-hole after a run of 
some length. For ordinary ore-smelting, producing a matte be¬ 
low 50 per cent, copper—usually between 33 and 40 per cent.— 
no arrangement can approach the modern fore-hearth for con¬ 
venience, economy, and safety; nor can the solid brick base just 
described compare with the simple iron drop bottom, as used in 
cupolas devoted to the melting of pig-iron or castings. A most 
useful modification of this fore-hearth is shown in the illustra¬ 
tions of the Herreshoff furnace. The profession is indebted to 
Mr. J. B. F. Herreshoff for thi is as well as for several other im¬ 
provements in connection with this furnace. The author also 
desires to express his obligations to the same gentleman for many 
valuable practical suggestions that he will not attempt to specify 
in detail. The fore-hearth or “ well ” is here placed on wheels, 
for convenience of removal, though more frequently it rests upon 
the solid ground. 

Another feature of especial value is the arrangement of the 
bottom of this furnace, which consists merely of a circular, con¬ 
cave cast-iron plate, firmly bolted to the lower border of the 
water-jacket, which extends some twelve inches below the tuyeres. 
This bottom is covered with a single course of fire-brick, resting 
on a shallow layer of sand, and might seem to be but a feeble 
barrier to such material as molten ore. It would, in fact, last 
but a very short time, were it not that the outlet of the furnace, 
through which all its liquid contents must pass, consists of a 


* The best example of this interesting but somewhat antiquated practice, 
though executed in brick furnaces, is found at Ely, Vermont, where there 
are some eight furnaces for the production of pig-copper in the manner in¬ 
dicated. 



196 MODERN AMERICAN METHODS OF COPPER SMELTING. 


4-inch by 7-incli circular opening through one side of the water- 
jacket, and is consequently so protected that the slag and matte 
can cut their way no deeper than the lower rim of the opening. 
There stands, therefore, constantly within the furnace a pool of 
molten material at least as deep as the lower border of the orifice 
referred to, while the constant loss of heat therefrom by radiation 
through the thin bottom of the furnace speedily converts it into 
a solid and permanent block, which need only be removed when 
cause exists for detaching the bottom. The most novel feature 



HERRESHOFF NEW FURNACE. 


of this arrangement consists in a similar opening in the back 
wall of the movable fore-hearth, which, being also protected by 
a small separate water-jacket plate, and backed up until it exactly 
meets the furnace opening, forms a .continuous, though very 
short, water-cooled channel from furnace to fore-hearth. The 
slag discharge of the latter is several inches higher than this 
channel, so that when the well is full and slag begins to run over 
into the pots, the opening just described is covered several inches 
deep with liquid material, which stands at the same depth in the 







































































































































































































































































THE SMELTING OF COPPER. 


197 


interior of tlie furnace as in tlie fore-hearth, except in so far as 
lowered by the pressure of the blast. The wind is thus com¬ 
pletely trapped, and its constant blowing through, which is one 
of the most common and obstinate annoyances of blast-furnace 
practice, is effectually prevented. 

The products of the fusion, usually only two in number in 
copper smelting, separate in this large fore-hearth very com¬ 
pletely, the matte settling quietly to the bottom, while the slag 
Hows through the anterior spout in a constant stream. When 




HERRESHOFF NEW FURNACE. 


globules of matte begin to appear in the slag stream, as evinced 
by the sparkling of the same while falling into the pot, and its 
greater liquidity when a small portion of the suspected slag is 
caught in a shovel and inclined from side to side while cooling, 
the tap-hole in the side plate is opened with a pointed steel bar, 
driven in with a heavy hammer if necessary, and the metal al¬ 
lowed to flow into molds of sand or, in some cases, of cast-ii on. 

When the well is thus empty and the communicating channel 
between furnace and fore-heartli uncovered, the blast escapes 



















198 MODERN AMERICAN METHODS OF COPPER SMELTING. 

through the same with full force, chilling the surface of the slag 
in its passage, and hurling glowing fragments of coke and glob¬ 
ules of molten ore in every direction. This is completely obvi¬ 
ated in the Herreslioff system by plugging the slag-spout open¬ 
ing with a ball of plastic clay heavily weighted. The fore-liearth 
being tightly covered with slabs formed of fire-brick held together 
by iron clamps, the blast is in this way entirely confined to the 
interior of the furnace, while the fore-hearth soon fills, and the 
wind is trapped as before. 

Still another convenient feature is shown in the arrangement 
by which the matte, when tapped, is kept free from the after¬ 
coming slag, of which a considerable quantity is present in the 
interior of the furnace and well, even after the appearance of 
matte at the slag-spout. As it is sometimes impossible or unad- 
visable to close the tap-hole at the exact moment when the last 
of the matte has escaped and the first of the slag begins to fiow, 
Mr. Herreslioff has arranged a tilting iron launder between the 
matte-spout and molds, which, when held up by a chain passing 
over a pulley, conducts the liquid to the regular molds, but when 
released by a catch, turns upon a horizontal pivot, and conveys 
the slag in the opposite direction and into compartments in the 
sand, where it is obtained in proper shape for re-smelting.. 

Brick fore-hearths of various patterns, but in the main re¬ 
sembling the type just described, have been in use in smelting 
sulphide copper ores for some seven or eight years, and are cer¬ 
tainly superseding all other arrangements. A brick fore-hearth 
of this description, strengthened by iron plates cast dishing to 
prevent cracking, and firmly bolted together through projections 
at the corners, will last, according to the quality of the products 
and the rapidity of the process, for from two to thirty days, a 
week being perhaps the average life. Their destruction is 
brought about in two ways: by gradual chilling about the sides 
and bottom until the cavity becomes too small or tapping is ren¬ 
dered impossible 5 or by the cutting away of the brick lining from 
the action of a hot basic slag and a low-grade ferruginous matte. 
The former condition results usually from the presence of a sili¬ 
ceous, infusible slag, especially when accompanied by a matte of 
high grade, which, from its high conducting qualities, has a 
strong tendency to chill. It is also especially influenced by the 
rapidity of the smelting process, a quick run with a large stream 


THE SMELTING OF COPPER, 


199 

of hot slag and metal keeping a basin open where the fusion of 

only half the amount in the same time would chill it within a 

«/ 

few hours. Any long stoppage is particularly detrimental, and 
may spoil a new basin within the first few hours. 

Even under the most favorable conditions possible, a certain 
minimum capacity, about 20 tons in twenty-four hours, seems 
absolutely essential to the employment of the brick fore-hearth, 
and this minimum only if the matte is tolerably low grade—be¬ 
low 36 per cent. As this amount can usually be treated even in 
the smallest furnace likely to be erected, the conditions that for¬ 
bid the employment of the brick fore-hearth do not often occur 
in the smelting of sulphide ores. 

While the u chilling up ” or u cutting out ” of the old form of 
crucible in the interior of the furnace involved a costly and tedi¬ 
ous series of operations, comprising the blowing out and cooling 
down of the furnace, the exterior basin can be taken down, re¬ 
placed, and dried ready for work within a few hours; and it is 
here that the advantages of this method of practice become most 
apparent, as the stoppage of the blast for this short period causes 
little or no trouble in the furnace itself. The arrangement of the 
fore-liearth on wheels is a notable convenience, as the exchange 
can be made with great facility, and the new basin, heated to red¬ 
ness by a coke fire, is pushed into place between the two guid¬ 
ing rails, a gasket of clay being interposed between the respective 
abutting faces, to prevent the leakage of the liquid product. As 
soon as the connection is made between the main pipe and the 
diminutive jacket on the back plate of the fore-hearth, the clay 
plug with which the main orifice into the furnace was closed is 
pierced, and the process goes on with the slightest possible de¬ 
lay* 

After cooling the interior of the old fore-hearth with water, 
the iron plates are removed and the chilled mass broken into 
fragments for re-smelting. 

The chill usually consists of a mixture of slag and matte, and 
is seldom so difficult to handle as to require the aid of blasting 
powder. This condition, when present, usually results from the 
deposition of metallic iron, which is sometimes found several 
inches thick and in a fine-grained, massive condition. It is best 

* The time consumed in the above operation, as taken twice under ordi¬ 
nary circumstances, was 18 and 21 minutes. 



200 MODERN AMERICAN METHODS OF COPPER SMELTING. 


treated by exploding a cartridge of the strongest Giant powder 
upon it, though drilling is sometimes necessary. A ratchet-drill 
is used for the purpose, and a sample of borings from such a 
chill, analyzed for the writer by Mr. A. F. Glover, Ph.D., had the 
following composition: 


Sulphur. 4-64 

Copper. 9‘80 

Iron. 82’70 

Carbon. 1’12 

Arsenic. 0 '41 


Slag. 0’78 

Nickel and cobalt. 0’81 


100-26 


This substance may be felt as a sticky, glutinous, semi-fused 
mass in the bottom of the basin, and is often scraped out in con¬ 
siderable quantities after tapping. The life of the basin is also 
often prolonged by a systematic chiseling out of the sides, front, 
and bottom, whenever empty, and a careful and energetic fur¬ 
nace-man will keep his fore-hearth in condition for a very long 
time. 

The c hillin g of the basin is counteracted by anything that 
checks the radiation of heat therefrom, and a backing of two 
inches of asbestos between the brick lining and iron plates is re¬ 
ported by Mr. Herreshoff to effect good results. The winter has 
used a mixture of wood ashes and crushed porous slag with good 
effect. The size of the basin varies according to the conditions 
of the case and the fancy of the metallurgist. A rectangle of 
28 by 30 inches and 28 inches deep will be found convenient. It 
should contain from one to two tons of matte, and when inclined 
to chill, should be made larger at the commencement rather than 
under contrary conditions. 

The amount of ore treated in water-jacket furnaces of the 
same size and with exterior basin differs greatly, according to its 
fusibility, the quality of fuel, and numerous local conditions. A 
few examples from practice will assist in forming an estimate. 

Herreshoff’s first water-jacket at the Laurel Hill Chemical 
Works, Long Island City, is shown in the accompanying illustra¬ 
tions. 

Wendt says: “ In front of the water-jacket A , the fore-liearth 
B is placed on wheels, and can be readily removed from the front 
of the furnace. The molten material flows directly from the 
shaft through the opening E into the fore-hearth. The joint be¬ 
tween the two is readily made or severed; for it consists simply 











THE SMELTING OF COPPER. 


201 


•of two water-jacketed faces of iron, which are placed in contact 
by moving the fore-hearth B against the jacket A. The cooled 
moil surfaces immediately chill any matte or slag liable to run 
between them, and make a perfect joint between furnace and 
fore-liearth. The first furnace erected was round, and 48 inches 
in diameter. Figs. 29 and 30 illustrate its construction. 

“ The water-jacket A rests on four posts attached to the bottom 
by brackets, as shown in the cut. C is. fire-clay rammed into the 



bottom on a supporting cast-iron plate, fastened to the furnace; 
I) is the wind-box; H the entrance of cooling water 5 I the exit 
of same 5 0 the cliarging-door; B the rectangular fore-hearth 
with fire-brick sides, top, and bottom, held by an iron plate-cas¬ 
ing ; K a layer of slag; F the cinder-lip ; and G the tap-hole for 
the matte in the fore-hearth. The second furnace, built at the 
Laurel Hill Works, was of the same circular shape, but 60 inches 
diameter. Blast was furnished at the usual low pressure by a 






























































































































































202 MODERN AMERICAN METHODS OF COPPER SMELTING. 

Baker blower, and trouble was experienced by the failure of the 
blast to reach the center of the furnace. 

“ The last furnace erected, and the one now in use, shown in 
Figures 31, 32, and 33, is rectangular in shape, with corners 
rounded, and the lines between the corners slightly curved or of 
convex shape. The height is ten feet, width 3 feet 7 inches at 
the bottom, and 4 feet 7 inches at the top, by 0 feet 4 inches 
length at the bottom, and 7 feet 4 inches at the top. The water- 
jacket is exceptionally narrow, having a water-space of only 2 
inches. 

“ Referring to the cuts, A is the body of the furnace; B a ring 
2 by 2 inches, to which the plates of the water-jacket are riveted. 
At the top C, the outer plate is flanged 2 inches, and the inner 
plate 4 inches, and the flanges then riveted. The bottom of the 
furnace E is a disked cast-iron plate 1.} inches thick, fastened to 
the ring B by tap-bolts. This permits the dropping of the bot¬ 
tom if required. The legs F are bolted to the ring B on the out¬ 
side of the furnace, thus not interfering with the dropping of the 
bottom. The hole G is the outlet of the furnace for both slag 
and matte. It is 9 inches high and 7 inches wide, and made bj 
riveting the wrought-iron frame H into the shell of the furnace. 
The furnace is blown by 13 tuyeres, five on each side and three 
on the back. They are placed 26 inches above bottom plate, and 
are two inches in diameter.” 

The construction of the furnace proper is practically identical 
with that of the original round furnace, but the fore-hearth is 
considerably changed. In the round furnace (see page 201), the 
fore-hearth was floored with a layer of slag-wool and brick as de¬ 
scribed. A brick lining was also used. The bottom of the brick 
lining was some 12 inches below the outlet from the jacket. Ex¬ 
perience proved that this bottom invariably chilled to a level with 
the bottom of the opening to the furnace. The cutting of the 
brick lining at a higher level also gave occasional trouble. Both 
these faults are avoided in the present construction. The for¬ 
mer, by raising the fore-hearth on high wheels A, and making 
the floor of the bottom lining within 2 inches of a level with the 
bottom of the inlet L. The latter, by entirely casting aside fire¬ 
brick lining and depending on the circular cast-iron water-jacket 
K. The tap-hole R in the shaft of the furnace is used only 
when blowing out to tap the furnace clean, or, sometimes, for 


THE SMELTING OF COPPER. 


203 


such small quantities of black copper as may be accidentally made. 
In the fore-hearth, the tap-hole 0 is the one commonly in use. It 
is made of copper, bolted to the iron body of the fore-hearth, and 
is water-jacketed similarly to the “ Liirmann ” slag tuyere of iron 
furnaces. The manner of operating it is also similar. M is the 
slag-spout j Ik, a brick-lined, dish-shaped movable iron cover of 
the fore-hearth. When smelting, the well or fore-hearth is 
wheeled up against the furnace, as shown in the cut, and a very 
small amount of wet fire-clay is placed on the iron faces sur¬ 
rounding the holes G and L, in order to make a tight joint be¬ 
tween them. 

In practical operation, after the furnace has been properly 
charged, the blast is let on. The first cinder collects in the bot¬ 
tom of the furnace shaft proper, and accumulates until it reaches 
the holes G and L. It then overflows rapidly into the fore-hearth, 
carrying matte with it. In a short time, the level of the molten 
material rises above the top of the hole X, and from that time on¬ 
ward the blast in the furnace can no longer blow out through L, 
and is completely trapped. Owing to the pressure of blast, the 
level of molten matte and slag in the fore-hearth is several inches 
above that in the furnace proper. Eventually the slag-lip M is 
reached by the cinder, which then overflows quietly. Matte is 
tapped periodically from the tapping-notch 0 without stopping 
the furnace. Matte is never allowed to accumulate until it over¬ 
flows at the slag-lip, the practice being to tap at stated intervals. 
The notch 0 is opened by a small steel bar, and pure matte, to 
the amount of about 1,000 pounds, is allowed to run off. Dur¬ 
ing this operation, the level of the molten slag in the fore-hearth 
falls, but not sufficiently to admit of blast escaping through L. 
By the simple insertion of a small clay stopper, the matte is 
stopped before cinder appears, thus avoiding all cinder picking. 
The whole process only occupies a few minutes, and is so perfect 
that for months a miss in tapping or closing up has not been 
made. 

The large amount of molten slag and metal in the fore-hearth 
greatly facilitates a clean separation, as the slag analysis clearly 
shows. The high percentage of the matte, made without trouble 
from ironing, is entirely due to the great rapidity of the smelt¬ 
ing. Standing at the charging-floor, the charge sinks visibly 
while watching it, and is exposed so short a time to the action of 


204 MODERN AMERICAN METHODS OF COPPER SMELTING. 

reducing gases that the iron is slagged before reduction, and thus 
ceases to be the obstacle to a rapid concentration of copper in a 
high-grade matte that metallurgists usually consider it. 

The following data of work, done by the different sizes of 
furnaces, speak for themselves. The saving in fuel by the larger 
furnaces is apparent. 


AVERAGE CHARGE PER DIEM. 


48 -inch furnace. 

60-inch round furnace. 

liectangular furnace , 

Roasted ore..51 *7 tons 

76’0 tons. 

76-8 tons. 

Raw tines.... 4*3 u 

8*0 “ 

13-2 “ 

Sand. 2 - 8 “ 

12-0 “ 

5-3 “ 

Iron slag. 

9-5 “ 

.... 

Total stock, 58 *8 “ 

105-5 “ 

95-3 “ 


Coke.11*5 tons or 20 %. 17’G tons or 16 %. 17‘4 tons or 18 %. 

The cost of smelting in the large Herreshoff furnace is very 
low r . The number of employes per diem is ten, and with gas- 
liouse coke at $2.50 a ton, and repairs exceptionally low, the total 
cost per ton of ore cannot aggregate 80 cents, or, on the ton of 
50 per cent, matte, about $10; or 1 cent per pound of copper 
contained. 

A 42-inch jacket with five tuyeres and one-half-pound blast at 
Stratford, Vermont, smelts from 40 to 45 tons of roasted pyri- 
tous ore, which yields a monosilicate slag and a matte averaging 
30 per cent, copper. 

The 42-inch water-jacket of the late Chemical Copper Com¬ 
pany at Phcenixville, Pa., with tuyeres and blast as in last ex¬ 
ample, smelted from 35 to 50 tons daily, according to the charac¬ 
ter of the charge. 

In Butte City, Montana, a 48-inch wrought-iron jacket, with 
six 2-inch tuyeres and five-eighths of a pound blast, smelted from 
60 to 65 tons daily of calcined pyritic concentrates, largely in a 
fine condition. In this instance, the richness of the ore, com¬ 
bined with a quite thorough calcination, gave such a high grade 
of matte as to render the employment of an external fore-hearth 
an impossibility, in consequence of the rapid chilling of the 
metal, which soon closed the tap-hole effectually, and in thirty-six 
hours reduced the basin to too small a size, which difficulty lias 
been obviated by substituting aiq “ Orford ” fore-hearth, wfith au¬ 
tomatic tap, to be described later. 











THE SMELTING OF COPPER. 


205 


These are average results, the fuel in all cases being coke of 
good quality, with from 12 to 15 per cent, ash, and the ores 
rather basic than siliceous. The performance of the same type 
of furnaces when producing pig-copper from oxidized ores will be 
noticed later. 

By inexperienced metallurgists, the general construction and 
arrangement of the water-jacket furnace may safely be left to the 
manufacturers, several of whom have had a wide experience in 
this matter. The quality of the material to be used has already 
been noticed, nor is it good management to economize in this 
particular. 

The water-jackets are usually made from sheets of iron or 
steel, rolled to the proper size, to avoid unnecessary riveting, and 
the rivet-lieads on the inside of the shaft should project as little 
as possible, to avoid burning off. 

The closing in of the water-space at top and bottom is effected 
by bending over and riveting the sheets together, or better, by 
the introduction of a circular ring of 2-inch square wrought-iron, 
forming a solid frame, through which the rivets pass, holding the 
iron plates firmly in place. A similar arrangement of cast blocks 
is provided for the tuyere openings, the castings having a central 
orifice of the proper size for the tuyere and a circular row of per¬ 
forations for the passage of the rivets. The tuyere openings are 
usually equally spaced, and from 18 to 20 inches from center to 
center. 

A convenient arrangement for the distribution of the wind 
consists in a cast-iron wind-box surrounding the furnace and in 
air-tight communication with the tuyere openings, the blast en¬ 
tering the former from the main wind-pipe. In the Herreshoff 
furnace, the tuyeres are rendered easily accessible by a circidar 
hinged plate opposite each, and provided with an eye-glass. In 
other cases, the tuyeres consist merely of galvanized iron pipes, 
connected with properly placed branches from the circidar main 
blast-pipe surrounding the furnace, though independent of the 
latter.* 


* Professor Richards, of the Massachusetts Institute of Technology, has 
improved on the above by the use of an ordinary steam-pipe of the proper 
size, which is ground slightly tapering, to make a tight joint in the tuyere 
opening, while a tee at the opposite end provides for the connection with 
the overhead blast-pipe, as well as for a glass eye-piece. 




206 MODERN AMERICAN METHODS OF COPPER SMELTING. 

The connection between blast-pipe and tuyere-pipe is usually 
made by the so-called tuyere-bag, consisting merely of a light 
duck hose, soaked in alum-water to render it uninflammable and 
impervious to the wind. 

The height of the furnace depends on the quality of ore and 
fuel, as well as the nature of the process; refractory, siliceous 
ores, and dense, strong coke or charcoal permitting and requiring 
the employment of a much higher furnace than the opposite con¬ 
ditions. As the greater number of water-jackets running on sul¬ 
phide ores in this country are favored with a basic and easily 
fusible charge, any height above 10 feet—from tuyeres to charge- 
door—is rarely met with; and even when smelting more infusi¬ 
ble material, the danger of reducing metallic iron and the gen¬ 
eral unmanageability of a high furnace would render of doubtful 
value any increase of the height beyond 14 feet. 

The arrangement of the upper portion of the furnace will de¬ 
pend principally upon the ultimate disposal of the smoke and 
fumes. The simplest and cheapest plan consists of a strong 
sheet-iron stack, lined with a single thickness of fire-brick, and 
erected upon the same columns that support the jacket itself. 

Such an arrangement could hardly be permanent, as the flue- 
dust from any material worth smelting should be sufficiently 
valuable to pay for saving. As this usually involves the leading 
of the furnace gases down to the level of the ground, it is custom¬ 
ary to effect this by means of a so-called “ down-take,” consisting 
of a vertical or inclined flue, leading from the furnace at a point 
above the charging-door to the entrance of the condensation- 
chambers or subterranean flue system. 

The charging-door should be proportionate in size to the fur¬ 
nace, and should open from 12 to 18 inches above the cliarging- 
platform, to insure the proper feeding of the furnace; for dis¬ 
honest laborers find it more convenient merely to push the ore 
into an opening level with the floor than to scatter it in the care¬ 
ful and systematic manner so essential to the regular working of 
the furnace. 

In cases where the occurrence of zinc-blende or even galena 
in the ore renders the formation of wall-accretions a matter of 
probability, it will greatly facilitate their removal to have the 
cliarging-door in the sloping roof-shaped housings above the fur¬ 
nace shaft, as long bars can thus be introduced with ease. This 


THE SMELTING OF COPPER 


207 


opening should he provided with a close-fitting door, and an easy- 
working iron damper should be placed in some accessible part of 
the chimney or down-take, a great diminution of flue-dust being- 
observable when the rapidity of the chimney draught is so 
checked that the fumes are barely carried away. 

The difference is obvious between the conditions in cupola 
practice, where the draught merely serves to remove the fumes 
produced, while the combustion results entirely from the blast 
below, and reverberatory work, where the burning of the fuel, 
and consequently the temperature, depend solely on the draught 
produced in the chimney. 

The ordinary shape of the American water-jacket is that of 
the frustum of an inverted cone or pyramid, the upper diameter 
being from 8 to 12 inches greater than the lower, while the use 
of boshes is very rare, owing to the causes already mentioned as 
influencing the height of ordinary furnaces. 

A slight bosh would be quite in place in smelting refractor}" 
ores, and is used to advantage in the Bell furnace at Butte City, 
where a very siliceous charge is smelted with poor charcoal. 

Where condensation-chambers or long flues exist, the size of 
the chimney seldom stands in any exact relation to the require¬ 
ments of a single cupola; but where no such passages are inter- 
posed / any data of the capacity of stack necessary for a furnace 
of a given size are useful, especially in the case of blast-furnaces, 
where, owing to reasons already mentioned, the ordinary rides 
governing the subject cannot be applied. 

For a single circular chimney, either directly above the jacket- 
shaft, or communicating with the same by a non-descending flue, 
experience shows that the ratio between the diameter of the 
chimney and the furnace diameter at the tuyeres should be 
about as 2 to 3. Thus, a 36-inch furnace requires a 24-inch 
stack • a 60-inch furnace, a 40-inch stack, etc.* 

Any considerable lessening of this ratio is likely to interfere 
with the draught and give rise to an annoying and injurious es¬ 
cape of gas from the charging-door. 

* If the sizes of chimneys here given seem unnecessarily large, it must 
he remembered that, when in good condition, the blast-furnace is so cold 
on top as to permit the introduction of the naked hand, and consequently, 
the temperature of the column of air in the stack is so low as to cause but 
little difference in weight between the interior and the exterior. 



208 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Tlie following measurements have been taken from stacks in 
various works in the United States, being selected from a consid¬ 
erable number: 


Diameter of furnace at 
tuyeres, in inches. 

Diameter of stack, 
in inches. 

Resulting draught. 

42 

30 

Excellent. 

40 

24 

Fair. 

36 

20 

Feeble. 

48 

30 

Feeble. 

48 

36 

Excellent. 


The last two measurements refer to the same furnace, the 
draught being so poor with the smaller chimney as to require its 
enlarging. 

While an elevation of a few feet above the roof is sufficient to 
carry off the fumes, safety demands that cupola stacks should 
have such a height that, during the blowing in and out of the 
furnace, the sparks and burning fragments of fuel that are then 
projected in considerable quantities shall be carried to a proper 
elevation. 


The water-jacket furnaces employed for the fusion of oxidized 
ores do not differ in any essential particulars from those just de¬ 
scribed. Being used principally in Arizona, New Mexico, and 
other distant parts of the country, where mechanics’ and masons’ 
labor as well as fire-brick and similar refractory materials are 
very dear, these furnaces are so arranged as to be almost entirely 
independent of those sources of expense after their first erection. 
This is effected by the use of heavy sheet-iron housings for that 
portion of the structure above the upper edge of the jacket, upon 
which fits a chimney of the same material, the iron in every case 
being protected by a 4-inch thickness of fire-brick, properly 
shaped to form the circle. 

Instead of the exterior crucible or fore-heartli just described, 
the Western water-jackets are for the most part provided with a 
cylinder of boiler iron, which projects downward below the 
jacket, forming an extension of the same, and provided with a 
falling bottom, consisting of two hinged iron doors, which, when 
supported in place by an iron bar, form a foundation for the sup¬ 
port of the quartz bottom, while the cylinder referred to is lined 
with fire-brick, thus forming an interior crucible, the full size of 















THE SMELTING OF COPPER. 


209 


the furnace, and extending from 16 to 24 inches below the tuyere 
openings. 

In rare instances, the water-jacket is continued to the extreme 
bottom of the crucible; but when handling a product so inclined 
to chill as is metallic copper, the arrangement just described is 
probably the best. 

The peculiarly favorable composition of the Copper Queen 
and many other of our Southern carbonate ores, being entirely 
oxidized, and containing an ample proportion of iron and lime, 
has permitted the employment of low, cheap furnaces, as well as 
the fusion of an unusual amount of ore in proportion to their 
size. And it is to this favorable condition of affairs, rather than 
to any inherent virtue on the part of the furnaces used, that the 
extraordinarily long and successful campaigns of the Copper 
Queen and neighboring furnaces must be attributed* 

The following figures, taken from Mr. Douglas’s paper, are 
average results of regular work : 

The Copper Queen smelter contains two 36-inch circular 
wrought-iron jackets, each of which puts through from 45 to 50 
tons of ore daily, flux being seldom required. To these a 
150-ton water-jacket has lately been added. 

The very fusible ore of the Old Globe mine (Arizona) is 
smelted in a 3-foot furnace at the rate of 55 tons daily, and even 
this extraordinary result has been exceeded by the United Yerde 
furnace. 

In nearly all cases, a No. 4J or 5 Baker*blower is used, which, 
at from 100 to 115 revolutions, supplies from 5 to 7 tuyeres with 
wind at a pressure of from 10 to 12 ounces. 

The size of the tuyeres is very variable, 3 inches being the 
average diameter, although the Copper Queen management has 
found a decided advantage, both in capacity and in freedom of 
the slag from copper, by increasing this measurement to 5 inches. 


* As the water-jacket, furnace lias had its principal development in the 
smelting of oxidized ores, and as its whole construction and management 
are peculiarly American, it seems proper to describe the same with some 
minuteness, taking as a type the plant of the Copper Queen mine, of Ari¬ 
zona, where, under the direction of Mr. Lewis Williams, it has been thor¬ 
oughly adapted to the surrounding conditions. Ample use will be made of 
the valuable paper by Mr. James Douglas, entitled “The Cupola Smelting 
of Copper in Arizona,” which was written for the United States Geological 
Survey, Albert Williams, Jr., editor. 



210 MODERN AMERICAN METHODS OF COPPER SMELTING. 


About 1,000 fire-bricks are required, on the erection of the 
furnace, for the lining of the portion above the jacket, and for 
the crucible. None is subsequently used, as the upper lining 


lasts indefinitely, while the crucible is kept from burning out by 
the introduction of siliceous or clayey ore through the tuyeres, 
whenever a too hot basic slag has thinned its walls and bottom 
beyond the normal standard. Any indications of chilling up are 
at once counteracted by a slight addition of fuel, and by per¬ 
mitting the flame to blow through the tap-hole and metal open¬ 


ing. 

These orifices, provided with cast spouts, are situated respect¬ 
ively 10 and 24 inches below the tuyere openings, the latter be¬ 
ing at the very bottom of the crucible. 

They are closed by inch bottom-plates, perforated with a large 
opening, the slag flow being cooled by water. Even without such 
cooling, these plates are found to possess decided advantages over 
the ordinary brick-work openings. 

The cooling water is introduced into the jacket through four 
14 -inch pipes, at some distance above its lower edge, and should 
be deflected at right angles from its horizontal course, experience 
having shown that its constant spouting against the hot inner 
iron plate causes a rapid perforation of the same. Where lime 
salts are present, it should never be allowed to reach a high tem¬ 
perature, on account of the formation of scale. 

The small quantity of water required after the furnace has 
reached its full burden, compared with what is necessary during 
the operations of blowing in and out, although usually attrib¬ 
uted to the formation of a coating of slag on the interior of the 
jacket, is, in the author’s opinion, due rather to transference of 
the point of greatest heat to the center of the shaft. This arises 
from the formation of slag, noses around the orifices of the 
tuyeres, by which the blast is conducted away from the walls, 
which are thus left comparatively cool. 

The large amount of water necessary to cool the Copper 
Queen jackets—some 40,000 gallons daily—suggests some rela¬ 
tion between that circumstance and the great size of the water- 
space in the jackets there used, being 9 inches wide at the bot¬ 
tom and 4f inches at the top. In the Herreshoff furnace, and 
three other jackets employed by the writer, the water-space has 
not exceeded 2 inches, and though the diameter of the furnaces 


THE SMELTING OF COPPER. 


211 


was considerably greater than that of the Copper Queen—all of 
them being above 42 inches—a single 2-inch pipe under a slight 
head was quite sufficient to supply the cooling water. This is a 
point well worth examining, especially where water is scarce and 


y, (is n our Souther n carbonate districts. It is possible that 
the impure nature of the Copper Queen water, requiring the re¬ 
moval through hand-holes of the calcareous deposit every five 
weeks, may necessitate the broad water-space used. 


THE MANAGEMENT OF WATER-JACKET FURNACES. 

The slight amount of brick-work in this type of furnace re¬ 
quires but a single night’s drying, a brisk fire being maintained 
in the crucible, upon which by four a.m. enough coke should be 
thrown to fill the furnace some 30 inches above the tuyeres, care 
being taken to secure an ample circulation of water through the 
jacket before the initial fire is kindled. 

By seven a.m. the coke should be in full glow, the combustion 
at first proceeding slowly, as its sole air supply comes from the 
open tap-liole and slag flow, but progressing very rapidly after 
once attaining the tuyere level. Instead of turning on a fight 
blast at this point, and gradually filling the furnace with alter¬ 
nate layers of charge and fuel, a much safer and more conven¬ 
ient method consists in filling the furnace level with the charge- 
door before using the blast at all, by which means all excessive 
heat is avoided.* 

A single exception may be made in favor of a small independ¬ 
ent tuyere, consisting of a 2-inch pipe connected with the blast- 
pipe by a canvas hose, which should be thrust through the breast 
opening in an oblique downward direction, the tuyere orifices be¬ 
ing tightly plugged, so that the flame may issue from the tap- 
hole—if such exist—while the whole interior of the crucible is 
brought to a white heat. Fresh coke being added until it stands 
some 30 inches above the tuyeres—which are left open—a charge 
of basic, easily fusible slag is given, alternating with coke charges 
in the ratio of three pounds of charge to one of fuel for the first 
three charges, after which the ratio may be changed to 4 to 1, 


* The method of blowing-in here described, though practiced for many 
years by the writer, has been recommended by a correspondent of the 
Engineering and Mining Journal , whose experience confirms the author’s 
views. 



212 MODERN AMERICAN METHODS OF COPPER SMELTING. 

while one-fourth of the slag is replaced by the regular ore mixt¬ 
ure ; this may be continued for two or three charges, when the 
relation of charge to fuel and of ore to slag should be again 
raised, reaching under ordinary circumstances a burden of from 
5J to 1 by the time the level of the charging-door is attained. 
Then, and not before, a light blast is turned on, and the rapidly 
sinking column replaced by constant charges of ore and fuel, the 
proportions between the same being regulated by the condition 
of the crucible and the appearance of the tuyeres and slag. 

It is a matter of great importance to make a good start, and 
especially where the brick fore-hearth is used to insure a rapid 
current of hot, liquid slag. A delay of a very few moments while 
the basin is first filling, or a thick, cold slag, will cause the for¬ 
mation of a chill that will very probably fill up the fore-hearth 
to half its extent. 

To avoid such a mishap, particular attention should be de¬ 
voted to the selection of the slag used for blowing in, and no 
fear need exist of its being too basic, provided the latter quality 
is due to oxide of iron and not to an excess of lime. For this 
purpose, nothing can excel the so-called “ metal slag/’ produced 
from the fusion of roasted matte, with the addition of just suffi¬ 
cient silica to produce a proper slag. While the percentage of 
Si0 2 in this material often falls below 22 per cent., no fear need 
be entertained but what it will become sufficiently acid in its pas¬ 
sage through the furnace to obviate any of those troubles that 
arise from the production of a subsilicate during ore smelting. 
The clay mortar and lining of the crucible and fore-hearth, the 
dirt that becomes mixed with it during transportation,, and, above 
all, the ashes from the fuel, will be found quite sufficient to neu¬ 
tralize any excess of base. By the gradual substitution of the 
ore-charge for this metal slag, a less and less basic slag is pro¬ 
duced, until the normal charge is reached, and the thin, blood- 
red, smoking, acrid slag that first appears is replaced by a white, 
steady, and slightly viscid stream, almost free from smoke—un¬ 
less unusually basic—and satisfactory to the experienced eye. 
In the water-jacket furnace this condition and the normal charge 
of ore and fuel should be reached within twelve hours, unless 
some drawback occurs, due to a neglect of some of the precau¬ 
tions already mentioned, or to a too rapid increase of blast or of 
the ore burden. Where sulphide ores are treated, the initial 


THE SMELTING OF COPPER. 


213 


charge should contain enough unroasted ore to produce a matte 
below 35 per cent, copper for the first two or three tappings. By 
tins means the fore-heartli is heated to the proper point, and the 
chilling due to too rich a matte at too low a temperature is 
avoided. 

here oxidized ores are treated, and an interior crucible used, 
the means already mentioned will secure a proper temperature 
and prevent chilling. 

But the exterior u steep ” crucible, although previously heated 
to redness by a coke fire, is pretty likely to become partially filled 
by a so-called “ skull,” or chill of metal, which fines the sides and 
bottom to the thickness of several inches, rendering it impossi¬ 
ble to tap and difficult to ladle. This chill should be allowed to 
form until the furnace has reached its normal condition, and slag 
and metal are flowing freely, when it may be removed by means 
of pointed bars and an overhead tackle. It leaves a glowing 
hot crucible, which, after a little repairing, is allowed to fill with 
the hot products, and is then carefully covered with a mixture of 
fine charcoal and ashes, by which means it is kept from chilling 
for a long period. 

The Copper Queen, and nearly all water-jacket furnaces run¬ 
ning on oxidized ores, are provided with an interior crucible, in 
which both slag and copper collect, the former being tapped into 
pots every six minutes, while the metal is run through the 14-inch 
lower spout every half-hour into iron molds, mounted on wheels, 
and which hold about 250 pounds.* 

The tapping is accomplished with great ease, using only a 
fight, pointed iron rod, the aid of the sledge being scarcely ever 
required. As the openings for both slag and metal are made in 
jacketed copper plates, they never become too large for easy 
plugging, and are stopped by a minute ball of clay. 

Where the ores are easily fusible and produce no wall accre¬ 
tions, and, above all, where constant supervision and extreme care 
are bestowed upon the smelting process, as at the Copper Queen, 
the length of the campaigns seems dependent only upon the fife 
of the machinery and jacket, although it is found necessary at 
these works to burn down the furnace to the tuyeres every five 

* In almost every case where Arizona practice is referred to, Mr. J. 
Douglas’s paper lias been consulted either for direct information or verifica¬ 
tion. 










214 MODERN AMERICAN METHODS OF COPPER SMELTING. 


weeks in order to remove the • calcareous sediment from the 
water-space. Still, as the crucible is not cooled off, and as the 
furnace resumes its normal condition as soon as refilled, these 
brief interruptions can scarcely be considered as terminations of 
a campaign. 

The conditions at these works are peculiarly favorable, no ex¬ 
traneous flux being required when proper proportions of ore can 
be obtained from the different levels, where calcareous, ferrugi¬ 
nous, and siliceous mixtures of carbonates and oxides of copper 
are all represented. The following analysis of the average 
slag for several months is taken from the report already 
mentioned: 


Per cent. 

Magnesia. 0‘20 

Alumina.15 "40 

Alkalies and loss. 4‘85 

100-00 


The average slag assays from the smelting of oxidized ores in 
water-jackets may be estimated at 1'75 per cent, copper, consist¬ 
ing of about equal proportions of oxidized and combined copper, 
and of minute metallic globules. 

A rectangular water-jacket, built for the Detroit Smelting- 
Works, Clifton, Arizona, by Mr. C. Henrich, presents certain in¬ 
teresting points for comparison. The cross-section at the tuyeres 
is 33 by 66 inches, while 10 inches above the same a bosh is be¬ 
gun, so that 30 inches above the tuyeres the cross-section is en¬ 
larged to 45 by 78 inches. The four lower cast-iron jackets ter¬ 
minate at this point, where they are surmounted by four others, 
which still diverge slightly, so that at their upper surface, 7 feet 
6 inches above the tuyeres, the furnace has an inside section of 
54 by 87 inches, which is retained to the charging-door, 10 feet 
6 inches above the tuyeres. The slag-tap is 6 inches below the 
latter, and the crucible is 14 inches deep, lined with brick, and 
provided with a drop bottom. There are fourteen 2f-inch 
tuyeres, five on each side and two at each end, receiving a 
blast of 10 ounces from two No. 44 Baker blowers, making 
115 revolutions. The object of the bosh is to increase the 
reducing action, with the view of obtaining cleaner slags, a 


Per cent. 


Silica.26-64 

Protoxide of iron.42-60 

Manganese. 0*30 

Zinc. 0*50 

Lime. 9*51 












THE SMELTING OF COPPER. 


215 


result tliat is claimed to have been obtained, the slags from 
this furnace assaying 04 per cent, lower than from the small 
perpendicular furnaces. There was also a saving in coke of 
8 per cent. 

The ores smelted are mixtures of carbonates and oxides, 
and, being slightly too siliceous, require the addition of a 
small proportion of limestone and iron to produce the follow¬ 
ing slag, an average of several weeks, as determined by Mr. S. 
James, Jr.: 

Per cent. 

Silica.34'34 

Protoxide of iron.32’27 

Manganese. 6‘24 

Lime.10*13 

Magnesia. 2*30 

An elliptical furnace, provided with sectional cast-iron jack¬ 
ets, forming a bosh 29 inches high immediately above the tuyere 
level, has been in use for many years for treating the slags re¬ 
sulting from the fusion of the Lake Superior metallic “ mineral” 
in reverberatory furnaces, previous to the refining operation, 
which is merely a later stage of the same fusion* (See section 
on Refining.) 

The cupola referred to is a modification of McKenzie’s pig- 
iron cupola, and has, in place of distinct tuyere-openings, a five- 
eighth inch slot encircling the entire furnace, just below the 
water-bosh. Below the tuyeres is a 34-inch deep crucible, nearly 
the full size of the furnace, and closed by a drop-bottom, pro¬ 
tected by a few inches of sand. The water-bosh consists of 
curved sections of cast-iron, fitted closely together, and five- 
eighths of an inch thick on the inner and lower sides, while 
the external and superior sides have only half an inch of 
metal. This bosh is 22 inches high, and is kept cool by a 
three-quarter inch supply-pipe, furnishing 25 gallons of water 
a minute. 


Per cent. 


Alumina.11*80 

Alkalies and loss, etc. 3*64 


100*72 


* The measurements and other details of these slag cupolas may he seen 
in the accompanying illustrations, which first appeared in connection w T ith 
Prof. T. Egleston’s paper on “Copper Refining in the United States,” pub¬ 
lished in the Transactions of the American Institute of Mining Engineers , 
Vol. IX., of which use is also made in the following descriptions, as verify¬ 
ing the writer’s own observations. 













Half Elevation 


Half Section E-E 


SLAG CUPOLA—ELEVATION, 









































































































































THE SMELTING OF COPPER. 


217 


The cupola is 7 feet 6 inches in height from tuyere level to 
charging-door, and has a greater axis of 7 feet and a smaller one 
of 4 feet 9 inches. 

A peculiar inverted siphon arrangement for the trapping of 
the blast during the continuous slag flow will be noticed by ref¬ 
erence to the illustrations. As even during the ten-hour cam¬ 
paigns made by these furnaces (owing to the small lots of slag 
belonging to separate mines), two of these slag flows are pretty 
thoroughly used up, they wall hardly be likely to come into gen¬ 
eral use. 

The material smelted is a siliceous slag from the reverbera¬ 



tory furnaces, carrying some 15 per cent, of copper and over 40 
per cent, of silica. About 20 tons are smelted in ten hours, using 
anthracite as fuel, brief attempts to use coke having resulted 
in an increase in the richness of the final slag. About 1 pound 
of coal is used to smelt 3 pounds of slag, probably the highest 
consumption of fuel in the United States. Blast is furnished by 
a No. Baker blower at a pressure of 10 ounces per square inch. 
The metallic copper produced is impure, containing some 5 per 
cent, of iron and half of one per cent, of sulphur, the latter com¬ 
ing from the fuel; while the large amount of iron present is also 
due to the powerful reducing action of the anthracite, which 











































Fig.3 



SLAG CUPOLA. 












































































THE SMELTING OF COPPER, 


219 


seems necessary to decompose the silicate of copper present in 
the slags* 

On account of the daily blowing ont of these furnaces for the 
reasons already alluded to, and the necessity of maintaining a 
strict separation of the material belonging to the various mines, 
the furnace bottom and sides, up to the water-bosh, are torn out 
and renewed every run. Although this practice is made neces¬ 
sary in order to obtain every scrap of copper-bearing material be¬ 
longing to each special campaign, still the deeply eaten and worn 
condition of the brick lining shows that metallurgical reasons 
also exist for this laborious and expensive custom. 

In common with the Arizona furnace managers, those at 
Houghton (Lake Superior) have also found that the slag flowing 
from the furnace contains an appreciable amount of copper in 
the shape of fine beads, technically denominated “ prills.” In 
both localities, recourse has been had to an independent fore- 
liearth, consisting of a rectangular iron box, in which the metal 
settles during the slow progress of the slag. 

This fore-hearth at Lake Superior is fined with a mixture of 
clay and sand, and is G feet G inches long, 3 feet G inches wide at 
the middle, and 2 feet 9 inches at each end, being slightly oval 
in shape. A considerable quantity of scrap-iron is placed in it 
at the beginning of the run, with the view of reducing to metal 
the oxidized copper contents of the slag, and is successful to the 
extent of saving some 10 per cent, more than when omitted. A 
cake of from 150 to 200 pounds is usually obtained from the 
daily run, from a charge of 20 tons of slag, yielding 15 per cent, 
of copper, the fore-hearth therefore saving about 2 h per cent, of 
the entire metallic contents. The slag from these cupolas is very 
clean, considering the grade of the product, and is reported to 
average below 0*75 per cent., rarely reaching one per cent. It 
is rejected as worthless. 

The fore-hearth in use at the Copper Queen furnaces for 
catching the entangled metallic shot is a rectangular box, made 
of four cast plates and mounted on small wheels. Its inside di¬ 
mensions are 4 by 2J feet, and 30 inches deep. It is lined with 

* The formation of so large an amount of silicate of copper during the 
primary smelting in reverberatories might possibly be prevented by the ad¬ 
dition of fine coal to the charge, although, of course, its fusibility would be 
somewhat lessened thereby. 




220 MODERN AMERICAN METHODS OF COPPER SMELTING. 

a mortar of clayey ore, and in an average life of 36 hours yields 
about 150 pounds of copper, besides the metal entangled in the 
chilled slag with which it becomes filled* 

The following table, compiled from the articles already ac¬ 
knowledged and from the writer’s own notes, exhibits compara¬ 
tively certain points of interest pertaining to the smelting of oxi¬ 
dized ores in water-jacketed cupolas: 


Name of Smelting Company. 

Area of furnace at 
tuyeres in sq. ft. 

Number of tuyeres. 

Total tuyere area in 
sq. ins. 

Pressure of blast in 
oz. per sq. in. 

Pounds of ore to 1 

pound of fuel. 

Pounds of ore to 1 

pound of charge. 

Tons of ore per 24 

hours. 

Tons of charge per 24 

hours. 

Detroit Refining "Works 


Continuous 







(Houghton, Mich.). 

24£ 

tuyere. 

134 

10 

3-00 


40-00 

56-00 

Copper Queen. 

7 

6 

75 

10 

5-90 

5-90 

47-00 

47 • 00 

Old Drum'ni on. 

7 

6 

64 

10 





Detroit C’r Co. large furnace 

11-8 

14 

83 

12 

6-55 

7-02 

79-15 

86-65 

“ “ small “ 

7 

6 

58 

10 

5 ’55 

6-00 

45-00 

48-60 

Ariz’naC’rCo. large furnace 

12-5 

6 

64 

10 

.... 

7-75 


75-00 

u “ small u 

7 

6 

58 

10 

.... 

7-75 


55-00 

United Verde. 

7 

6 

58 

10 

.... 

5-00 

52-00 



A noteworthy feature of the Arizona cupola practice is the 
purity of the product, averaging between 97 and 98 per cent, of 
metallic copper. Its freedom from injurious substances is, of 
course, due to the quality of the ore; but the low percentage in 
Aon of pig-copper, produced in many instances from highly fer¬ 
ruginous ores, and by a process of reduction so powerful that 
only traces of oxidized copper remain in the slag, must be at¬ 
tributed to the rapidity of the fusion. This in its turn results 
principally from the volume and pressure of the blast and suita¬ 
bility of the fuel, which consists in most cases of a coke of toler¬ 
ably good quality from Trinidad, Colorado, or San Pedro, New 
Mexico, the latter containing less ash, but being of a more friable 
nature. With Connellsville (Pennsylvania) coke, a slightly higher 
ratio of ore to fuel is obtained, and a patent Cardiff coke gives 
the best results of all. The average contents of ash in the Trini¬ 
dad, San Pedro, and Connellsville cokes is reported respectively 


* See section on Brick Cnpolas for other varieties of fore-hearth. 
































THE SMELTING OF COPPER. 


221 


at 14*6, 13*2, and 11*G per cent. Sufficient sulphur is present in 
nearly all the Arizona carbonate ores to form a small proportion 
of matte, which in many cases is simply thrown back into the 
furnace without further treatment, while other companies more 
sensibly sack and ship it East as a separate product. It varies 
between a high blue-metal and a low white-metal from 60 to 66 
per cent., and could be advantageously roasted twice in heaps 
and mixed with the ore-charge in small quantities. 

At the Copper Queen Works, a kiln is used for the roasting 
of whatever matte may be produced, though its occurrence is very 
irregular. Sometimes, for several successive days, as much as 
1,500 pounds per day will be made, and is easily separated from 
the bars of metal on which it floats. At other times, for months 
together, not a trace of matte will occur; nor does the depth 
from which the ore is mined have any influence on its produc¬ 
tion, for the sulphide ores which cause it are found fully as abun¬ 
dantly in the upper as in the lower levels. 

Even the freedom from all concentration and calcination proc¬ 
esses does not entirely relieve the Arizona smelters from that 
great curse of blast-furnace work—the occurrence of a consider¬ 
able proportion of fine ore. The clayey and friable nature of 
many of the ferruginous and calcareous carbonates favors the 
formation of fines, which, aside from the heavy loss entailed by 
their escape through the stack, clog the furnace, obstruct the 
blast, and, being sifted down between the coarser lumps of ore 
and fuel, reach the smelting zone in a cold and unprepared con¬ 
dition, causing the chilling of the crucible and the growth of 
long noses from each tuyere, which may meet in the middle, 
forming a central core of semi-fused material that may necessi¬ 
tate the termination of the campaign. The loss in flue-dust is 
partially remedied at the Copper Queen and one or two other 
furnaces by the construction of flues and dust-chambers. The 
clayey nature of most of the fines, and the hot and dry climate, 
assist the process of bricking these fines, although in certain 
cases an addition of milk of lime is found necessary to bind the 
particles together with sufficient firmness. 

Most of the ores being of a basic and decomposed nature, a 
very small amount of mechanical preparation for the furnace is 
demanded. At most works, the ore is merely passed through a 
jaw-breaker, set to a size of from 2 to 3 inches. 


222 MODERN AMERICAN METHODS OF COPPER SMELTING. 

For tlie reasons already enumerated, a height of the furnace 
from tuyere to charging-door of more than seven feet is rarely 
met with in this particular practice. 

The use of round or oval furnaces of the water-jacket type 
has become almost universal in copper smelting, probably owing 
to their ease of construction. A long and varied trial by the 
writer of almost every style and size of cupola was so indubitably 
in favor of the rectangular or elongated oval form, and more es¬ 
pecially of very much larger furnaces than any yet described, 
both for economical reasons and for ease and simplicity of man¬ 
agement, that the comparative want of success in certain reported 
cases is apparently attributable to other causes than a mere in¬ 
capacity on the part of the furnace to fulfill all expectations based 
on comparative calculations. The new furnace built by the 
Detroit Smelting Company, of Michigan, which is much larger 
than the older ones, is entirely satisfactory, and works ’with in¬ 
creased economy, reaching a result fully equal to its theoretical 
capacity. 

The great size of the furnaces preferred by the writer has, 
until quite recently, prevented the employment of water-jackets, 
so that their description and discussion must be deferred to the 
section on Brick Blast-Furnaces, but since the success of quite 
large, oval, wrought-iron jacketed cupolas has been assured, there 
can be but rare instances where brick furnaces would be pre¬ 
ferred. 

The life of a water-jacket in constant use depends so entirely 
upon its treatment and upon the quality of the feed-water that it 
is impossible to fix any exact limit for it. Cast-iron jackets iqay 
last from one to four years, though sometimes cracking in a few 
days, while wrought shells have been run almost constantly for 
six years without any considerable repairs. Under the most fa¬ 
vorable conditions, and in the lack of more extended experience, 
five years may be assumed as the duration of a wrought-iron 
jacket in constant use. 

Estimates of cost would be superfluous, the manufacturer's 
price-lists and cost of boiler work and piping supplying all need¬ 
ful bases for calculation. 

Owing to the comparatively recent introduction of water-jack- 
eted furnaces with improved arrangements for crucible and fire- 
hearth, there is a great lack of accurate information on the sub- 


THE SMELTING OF COPPER. 


Composition of slag. 

•no 

CO lO N CO 

■ *>D T* T—t 

. • * • 

t-h th o th t—i O 

e O s lV 

| 05 t- a 

1 C- ». a-. CO O. (M 

'0^0 

L— 00 

t-h O &• o» CO 

T—1 
* 

‘CRi 

CO i> CO CO 

CO JO 05 o- O CO t- 

CO lO O ^ CO ^ 

*01S 

JO 

CO 00 n rf • 05 SO 

1 W CO COCO CO CtTr 

CO 

Composition of 
product. 


Tt< t- 

S « ».(Ji ih o co 

s? * 

•no 

(0? O* CO iO Hie* 

. . . . . ai 

CD J> COCO t- r!H 

CO 05 05 05 05 CO 

- S 

O CO „ 

i o ^ 

tN i-i O * 

Charge per 
24 hours. 

1 JO 

•ptij o) oijuji ! ^ r?* °° 

1 05 00 0500 <® coco 

•suoj, 

Tt< «N» lO rHW< H|* 

CO O * T—1 SO 

Tf lO SO ^ t- *0) 

to CO 

3 
| E 

_o 

S—i 

o 

*[8UJ OJ OIJUH 

05 GO CO CO i'- CO iO 

N O NO Tt< CO CO 

•8U0X 

r-<|CJtO 

CO CO QC • -T-* CO GO 

O TT Tt'CO CO CO 

OJ 

•aomunj jo tqSpH 

: 

30 • 


He* ^W< 

CO t- 

•saqoui 8.limbs 
ui sojaftij jo T?9.iy 

rs> • 

rt< 


oT (Ncj 

69 ^ 

•sajoifm jo aaqiuuM | 50 : 


JO zo 50 

•J98J 

ojunbs in S0.iaim 
ju aoutunj jo U8.iv 

96 


iC 

O? lO CO 

00 O? 05 

v-H 

•[9UJ 

jo qsu jo ‘juso J8<j 

Oi • 

tH 


HCl 

Tf SO 

TH tH 

Character of 
fuel. 

Connellsvillecoke 


Trinidad coke... 

Connellsville coke 
Gas-coke. 

•qoui 

aaunbs J8d saound 

Ut JSUiq JO 8JUS88JJ 

■pi • 

CO 05 o O 

T—1 T—1 

Character of 
flux. 

Gravel. 

Metal slag. 

Siliceous car¬ 
bonates. 


C u pr i fer ous, 
hematite. 

Siliceous car¬ 
bonates . 

Metal slag.__ 

'a jo jo agujuaojaj 

He* 

CO tH go 

O* CO 

l i 

81 

m 

Character of 
ore. 

Calcined pyrites.. 
Western carbon¬ 
ates . 

Calcined matte... 

Calcined matte... 

Carbonates and 
oxides. 

Calcined pyritic 
concentrates ... 

Pyrites fines, un¬ 
roasted. 

•J9qmn^[ 

tH O* CO ^ JO CO i> 


Note.—N umbers 1, 2, ?, and 4 a v e from the same furnace. 

* These figures have been estimated. In all other cases, they are the result of actual determinations. 

The author is indebted to his various chemists and assistants at the different furnaces for most of the chemical results here given. 







































































224 MODERN AMERICAN METHODS OF COPPER SMELTING. 


^Wa/tez- ^jacfi c4 
Sl41,e{4il4^ eFu.'MtaCC 

vuitfv 

(£az{ V&<2 AX'l\,cW !> 
elm p£oi>eme/nC> 

fot 

Copper Ores. 


dt cm u fa ctu/tcA 

eFz-ci^c^ Sc GJWfWe'to. 

Cfucacp, el££., 

% s. a. 















































































































































































































THE SMELTING OF COPPER. 


ject, and any reliable details of their performance, capacity under 
differing conditions of blast and charge, etc., are valuable. On 
this account, the table given above, compiled from the records 
of practice, although not as full or complete as desirable, will 
still be found of value. 



BARTLETT WATER-JACKET—WATER-TANK ARRANGEMENT. 



































































































































































































CHAPTER X. 

BLAST-FURNACES CONSTRUCTED OF BRICK. 

The small type of brick cupolas, though not yet entirely 
abandoned in the United States, in the treatment of copper ores 
and mattes, has been described in almost every former work on 
this subject, and it possesses no peculiar or distinctive features 
that demand particular attention. 

The largest type of brick cupola as yet found unmistakably 
practicable and advantageous will be selected for detailed descrip¬ 
tion, the accumulated experience of several years, and covering 
almost every grade and variety of copper-bearing material, having 
emphatically demonstrated its economy and general superiority. 

That the bounds of economy have not been overstepped in 
this matter of size is evident from careful comparative experi¬ 
ments, which show conclusively that the cost per ton of ore in¬ 
creases, the repairs become proportionately greater, and the ease 
of management is sacrificed with every inch that is taken from 
the size already referred to. What the limits may be in the other 
direction is yet an open question 5 but experience has shown that 
any further considerable augmentation of capacity involves the 
solution of various new problems pertaining to the blast and to 
the handling of such large quantities of ore and slag, and certain 
other matters that will be noticed in their proper place. It would 
be unjust to attempt the history or description of the successful 
introduction of this form of large rectangular brick furnaces 
without mentioning the names of certain persons whose persever¬ 
ance and skill have overcome the difficulties inseparable from 
such an undertaking, and who have made to American metal¬ 
lurgy one of its most valuable additions* 


* The gentlemen referred to, Messrs. W. E. C. Enstis, R. M. Thompson, 
H. M. Howe, J. L. Thomson, are, or have been, all officers of the present 




BLAST-FURNACES CONSTRUCTED OF BRICK. 


227 

The distinctive peculiarities of the “Orford” furnace, as this 
altered and improved form of Raschette furnace is usually des 
ignated, aside from its unusual size, are the large number and 
diameter of its tuyere openings—14 of G inches diameterj the ab¬ 
sence of any interior crucible or space for the collection of the 
fused products; the substitution therefor of an exterior fore- 
heartli or basin, and the construction of the latter in such a man¬ 
ner that two continuous streams—of slag and metal respectively 
—flow therefrom into ordinary slag-pots, without any blowing 
through of the blast, or delay for tapping and other related ma¬ 
nipulations. The latter arrangement may be applied to any fur¬ 
nace of sufficient size, it being absolutely essential, for the pre¬ 
vention of chilling, that a large quantity of molten material 
should constantly traverse it. If the product is a matte of high 
grade, GO per cent, and over, a much larger quantity is necessary 
to prevent chilling than if the metal is of poorer quality. The 
rapid chilling of the former is due not to its possessing a higher 
fusion point, but because its capacity as a conductor of heat in¬ 
creases with its percentage of copper. 

When the smelting mixture is exceedingly rich, so that a 
very large amount of the copper-bearing product results, it is 
even possible, by rapid smelting, to maintain a constant stream 
of metallic copper—a practice that may be regarded as a curios¬ 
ity rather than as ordinarily feasible. 


Orford Copper and Sulphur Company, of Bergenport, New Jersey; and while 
the furnace referred to closely resembles the Raschette type of furnace so 
extensively introduced into Germany and Russia during the past thirty 
years, its management and all manipulations connected therewith are 
sufficiently different to convert into a brilliant success what has in Europe, 
at least, been practically a failure. The application of the exterior cru¬ 
cible, continuous matte-tap, and peculiar method of feeding and manipula¬ 
tion by which campaigns of a year are made with an excessively basic slag, 
and in the entire absence of any water-cooled tuyeres, aside from the treb¬ 
ling of its former capacity, are sufficient to constitute a valid claim to orig¬ 
inality. 

The writer is pleased to have this opportunity to acknowledge the bene¬ 
fits derived from long and intimate intercourse with these gentlemen, and to 
state that it was while occupying the position of superintendent of this com¬ 
pany that he first learned the full extent to which the cost of smelting could 
be reduced by increase in the capacity of furnaces. 




228 MODERN AMERICAN METHODS OF COPPER SMELTING. 

A detailed description of the construction and subsequent 
management of this form of furnace will bring forward the 




ORFORD BRICK FURNACE. 

points already referred to, and illustrate the practice that up to 
the present tune has been found most advantageous, and which 


PLAN. 



has cheapened the smelting of copper ores to a remarkable extent. 
The outside measurement of the furnace being 8 feet 5 inches 





































































































































































































































































































































































































































































































BLAST-FURNACES CONSTRUCTED OF BRICK. 


229 


by 16 feet 8 inches, an excavation should be made at the intended 
site some three feet larger in every direction than the figures just 
given, and of sufficient depth to reach solid ground and insure a 
proper foundation. A depth of 4 or 5 feet will usually suffice, 
the pit being immediately filled with concrete; or, where possible, 
the pit should be filled to nearly the surface with molten slag. 

The walls of the furnace should be begun a foot below the 
ground level, and should consist entirely of fire-brick up to the 
tuyere level, where the panels, shown in the cut, are begun. Up 
to this point, the walls are 30 inches thick, of solid fire-brick, 
while the panels are only 18 inches thick, thus being more acces¬ 
sible for repairs, and containing the tuyere openings. The rear 
wall is divided into three panels, equally spaced, and supported 
on each side by the full thickness of the wall, forming columns 
at each corner, and between the weaker portions, that are chiefly 
relied upon to carry the weight of the superincumbent structure. 
The panels are 30 inches wide and 33 inches high, and are 
strongly arched over with three rows of fire-brick, above which 
the full thickness of the wall (30 inches) is maintained to the top 
of the structure. Each panel is pierced by two 6-inch square 
tuyere-lioles, equally spaced, excepting the central front panel, 
which contains only a small orifice for the slag-run, at a point 
some 10 inches below the tuyere level. The panel referred to 
forms the breast of the furnace, and is not closed in until the last 
moment. 

The total number of tuyere openings is 14—6 behind, 4 in 
front, and 2 at each end. The interior rectangle is 3 feet 5 
inches wide and 11 feet 8 inches long, although any exact adher¬ 
ence to these measurements is unnecessary, the interior of the 
furnace being soon burnt out into an irregular shape and usually 
much larger than the size just given. 

Strong tie-rods, provided at then* extremities with loops, and 
buried deeply in the foundation, are placed in position as indi¬ 
cated in the cut. Unless the transverse rods can be placed at a 
depth of two or three feet below the surface, they should merely 
lie fastened into the wall by hooks, as they would certainly be 
melted away in time. 





mo NT VIEW. 



SCALE /a IN. TO THE TOOT 























































































































BLAST-FURNACES CONSTRUCTED OF BRICK. 


231 


The brick should be laid with the closest possible joints, and 
in a \ ei \ thin mortar made of half each of raw and burned fire¬ 
clay, ground exceedingly fine. 

Heavy railroad iron may be used for binders, and should be 
used rather more than less liberally than shown in the illustra¬ 
tion, as the expansive force is enormous when the furnace is in 
full heat, and any serious cracking tends greatly to shorten its 
existence. 

If fire-brick are expensive, the outside fining, above the 



SECTION A B. SE CTION EE 



SECTION CD . SECTI ON G H. 


THE ORFORD u RASCHETTE n FURNACE. 

panels, and to a depth of 12 inches, may be constructed of red 
brick, although this is not recommended. 

The usual height from the tuyeres to the threshold of the 
charging-door is 8 feet; but this, of course, may be varied to 
suit the character of the ore to be smelted. The charging-doors 
are three in number, and of large size. All further details of 
construction are plainly shown in the cut. 

The chimney should never be made smaller than here shown, 
and if a vertical down-take is used, connected with flues for the 
saving of the flue-dust, its dimensions should be increased one- 
third. The latter construction is much preferable to the simple 
vertical chimney, and is absolutely essential where anything but 
































































232 MODERN AMERICAN METHODS OF COPPER SMELTING. 

the poorest material is smelted, as the loss in flue-dust, owing to 
the enormous volume of blast peculiar to this practice, is very 
great—especially as a large proportion of the charge often con¬ 
sists of fine ore, it having been found that these large rectangu¬ 
lar furnaces are peculiarly adapted to the treatment of that ma¬ 
terial. 

The tuyeres consist of rather heavy, galvanized sheet-iron— 
No. 18—and are connected with the vertical branches of the 
main blast-pipe surrounding the furnace with thick duck tuyere- 
bags, soaked in a strong solution of alum, to render them less in¬ 
flammable and to fill the pores of the cloth. Their diameter may 
varv with the character of the ore under treatment, but is usually 
from five to six inches, the pipes being merely thrust a short dis¬ 
tance into the square orifices left in the brick-work, and made 
tight with plastic clay. 

There remains nothing in the construction of this furnace 
that cannot be plainly seen from the illustration, and the discus¬ 
sion of its management from the time when taken in hand by 
the smelter will now be proceeded with. 

It is frequently customary to form the bottom of a solid mass 
of fire-brick, placed on end, and brought up to within 10 inches 
of the tuyere openings, sloping slightly toward the slag-run in 
the center of the front wall.* 

The author has found the following method, practiced origi¬ 
nally by the Orford Company, far superior to any other, espe¬ 
cially where low-grade matte is to be produced, the most difficult 
of all copper-bearing materials to confine within brick walls. 

After filling in the foundation with beton to a foot below the 
ground level, the furnace bottom is begun by laying two courses 
of fire-brick on end, and with the closest possible joints. This 
still leaves a space of from 24 inches to 30 inches to bring the 
bottom to the proper height, which is filled in as follows: 

The furnace and foundation being thoroughly dried by at 
least four days’ brisk firing with brands and similar material, 
enough coke is dumped into the red-hot shaft to fill it to a point 
some three feet above certain temporary openings that should be 

~ The practice of hasing the bottom upon an arch built over an open 
space below must be strongly condemned, as it will simply result in the 
cutting through of the arch, and the total disappearance of all metal until the 
cavity is filled, making eventually a solid, but somewhat expensive, bottom. 




BLAST-FURNACES CONSTRUCTED OF BRICK. 


OQO 

-oo 


left in the brick-work while building. These openings corre¬ 
spond in size, number, and position with the permanent tuyere 
openings, except that they are some 8 inches lower and directly 
beneath the.regular orifices, which, for the present, are plugged 

with clay. 

•/ 

Some six or eight tons of calcined quartz crushed to the size 
of chestnuts and mixed with about 5 per cent, of fusible slag, are 
spread upon the coke; and as soon as the latter is properly on 
fire above the temporary tuyere openings, the blast-pipes are put 
in place, and a light blast is continued until the coke is burned 
away, and the sticky, half-melted charge threatens to flow into 
the tuyere openings. The unconsumed coke and excess of quartz 
are removed through the breast panel—which was built up tem¬ 
porarily of 4-inch brick-work; and the furnace, being tightly 
closed, is allowed to cool very gradually for twenty-four hours or 
more. 

If the operation is successful, the bottom will be as solid and 
infusible as can be made, nor will any attempt at the substitu¬ 
tion of basic material for quartz, in consideration of the probably 
highly ferruginous character of the slag to be produced, result 
in any improvement on the plan recommended. 

It is probably as good a bottom as can lie made, although, as 
will be later seen, it offers but little resistance to a hot low-grade 
matte, when produced at the rate of from 30 to 50 tons daily. 

The furnace being thoroughly dried and heated, blowing in 
may follow at once, it being only necessary to plug the tempo¬ 
rary tuyere orifices, fill the shaft with coke to a point some 3 feet 
above the permanent tuyeres, and allow the fire to ascend to these 
openings before filling the shaft with alternate layers of charge 
and fuel, and putting on a fight blast (one ounce). 

All this may be done the night before starting, and at the 
same time, if not before, the fore-hearth and siphon-tap * must 
be arranged. This consists of a rectangular box, some 4 feet by 
3 feet 6 inches, formed of cast-iron plates strongly bolted together 
at the corners, and fined with a brick wall 4J inches or 9 inches 
thick, according to the quality of the product. It is fastened 


* This is an entire misnomer, as the apparatus here referred to, as used 
for the continuous discharge of the metallic product, has nothing about it 
pertaining to the principles of the siphon. 




234 MODERN AMERICAN METHODS OF COPPER SMELTING. 

firmly to tlie front of the furnace, just at the slag-run in the cen¬ 
ter panel, the lower middle portion of the anterior front wall of 
that structure forming its posterior boundary. It is divided 
longitudinally by a 9-inch wall of fire-brick into a greater and 
lesser portion, the area of the two compartments being about as 
5 to 2, and the direction of the division wall being parallel to the 
;short axis of the furnace. 

The entire molten contents of the furnace discharge through 
a 2-inch by 4-incli opening (the slag-run) in the middle panel (the 
breast) into the larger of these two compartments, which is pro¬ 
vided with a slag-spout, bolted to the upper edge of the front 
plate, while it communicates with the smaller compartment by 
means of a 3-inch by 8-inch vertical slot through the 9-inch di¬ 
vision wall, about midway of its length and on a level with the 
floor of the fore-hearth. This smaller compartment also has a 
spout about 2 inches below the level of the spout belonging to 
the larger division, and on the outer side, instead of the end 
wall, for the sake of convenience. 

A thorough understanding of this very simple and inexpen. 
sive contrivance will render it very easy to appreciate its man¬ 
agement. 

When the breast-hole is opened, and slag and metal first be¬ 
gin to flow, the larger compartment is soon filled, as the. only 
means of communication between the two divisions of the fore¬ 
hearth is the closed slot in the lower part of the 9-inch division 
wall. 

The molten products separate according to the law of gravity, 
and slag is allowed to flow through the spout of the large com¬ 
partment until the drops of metal appearing show that it is filled 
with the more valuable product. The channel of communication 
is now opened by means of a crooked tapping-bar, and the metal 
flows rapidly through the same into the smaller compartment, 
until an equilibrium is established, and both divisions of the fore¬ 
hearth are partially filled with the matte, the communicating 
channel being far below the surface of the same, and conse¬ 
quently so situated that slag can never reach it unless it should 
sink below the metal, which is obviously impossible. 

As the furnace constantly discharges its stream into the larger 
compartment, the fore-hearth is soon filled again, the metal sink¬ 
ing to the bottom and standing at the same level in both divis- 


BLAST-FURNACES CONSTRUCTED OF BRICK. 


235 


ions, wliile the slag simply flows over the surface of the matte in 
the larger compartment. 

As soon as the matte reaches the level of the spout attached 
to the small compartment, it begins to flow into a pot placed to 
receive it, and by judicious manipulation, and if a sufficient pro¬ 
portion of matte is produced from the charge, a constant stream 
of each product may be kept running without difficulty. 

The management of this u siphon-tap ” requires considerable 
experience, as the matte stops occasionally without apparent 
cause, and requires a certain amount of manipulation and coax¬ 
ing to keep running freely. This is accomplished by slightly 
damming up the slag-spout, which soon forces an excess of matte 
into the smaller compartment, or by clearing out the communicat¬ 
ing orifice by means of a heated bar bent to the required curve. 

With matte of 50 per cent, or over, the principal difficulty is 
found in the gradual filling up of the fore-liearth by chilling, 
while a matte containing 20 per cent, or less of copper, and pro¬ 
duced in large quantities, has directly the opposite effects, thin¬ 
ning the fire-lining until the plates are endangered, and cutting 
awav the division wall until the two compartments are virtually 
thrown into one. 

But even under these circumstances, and as long as a vestige 
of the center wall remains, the separation of the matte and slag 
continues to be perfect, and by judicious repairing and nursing, 
a fore-heartli apparently in the last stage of ruin may yet do 
good service for many days. 

An opening through the division wall 18 inches high by 24 
inches wide, and Actually involving two-thirds of the separating 
brick-work, is not incompatible with a perfect separation. 

The larger compartment is provided with a tap-hole at its 
lowest boundary, and on the side opposite the matte division, 
and a large quantity of sand should always be at hand ready to 
make up into rough molds in case of any sudden necessity for 
tapping the furnace. 

This is especially the case when producing very low-grade 
metal; for owing to its corrosive action, and to the fact that the 
anterior wall of the furnace forms the posterior boundary of the 
fore-hearth, the entire contents of the former may escape into the 
latter in case of a break through the plates. It is at first some¬ 
what startling to have such an outbreak when the entire bottom 


236 MODERN AMERICAN METHODS OF COPPER SMELTING. 

of the enlarged and burned-out furnace has been excavated to 
the floor level, forming a crucible some three feet deep and per¬ 
haps 4 by 13 feet in size. Under such circumstances the empty¬ 
ing of the fore-hearth by tapping—or oftener by breaking 
through the plates or brick-work at some* point—may result in 
the irruption of some 12 to 15 tons of matte upon the floor of the 
cupola-house. The workmen soon become expert at controlling 
such outbreaks by means of dry sand in unlimited quantities— 
the approach of anything wet is like touching a match to a keg 
of gunpowder—and no serious results need be apprehended when 
the buildings are fire-proof, as should invariably be the case 
where large brick furnaces are employed. 

Such an outbreak is treated as are most other accidents to 
which this type of furnace is liable, by entirely shutting off the 
blast and allowing everything to stand quiet for a few hours. 
The orifice is tightly plugged from the outside, and the molten 
products that trickle into it from the interior are allowed to cool 
by standing still, until it is as tight as ever. 

The full burden may be reached after feeding two quarter 
charges, four half charges, and eight three quarter charges, slag 
being substituted for ore to a considerable extent, until the con¬ 
dition of the furnace warrants the employment of the normal 
mixture. 

This is shown by the gradual change of the color of the slag 
from a dull red to a yellowish white ; the entire ceasing or great 
diminution of smoke arising from the slag; a certain peculiar 
viscosity (except in very basic slags) when it falls into the pot; a 
general brightening of the tuyeres, succeeded by the formation 
of short noses, perforated abundantly with bright holes; and a 
steady and rapid sinking of the charge. 

Although the charging of the blast-furnace is always one of 
the most important manipulations belonging to this apparatus, 
it is doubly the case with the furnaces now under discussion. 

While the walls of the water-jacket are thoroughly protected 
and entirely unassailable, the mason-work of the brick furnace is 
completely exposed, and any error in the proportion of fuel to 
ore or in the manner of charging is sure to be followed by seri¬ 
ous results. 

This is, strange as it may seem, peculiarly the case with a sili¬ 
ceous charge, and nothing can more clearly illustrate the proper 


BLAST-FURNACES CONSTRUCTED OF BRICK. 


237 


method of working than a brief description of an irregularity 
that is constantly liable to occur, and that will be quickly recog¬ 
nized by all practical cupola smelters. 

An imaginary case will be assumed where a newly blown-in 
furnace, in good condition, but with a slightly too siliceous 
charge, begins to become too hot in one end, through some slight 
irregularity of feeding, or through an improper proportion of 
ore to fuel—either too much or too little of the same producing 
very similar effects. 

The attention of the foreman will be called to the fact that 
one of the end panels is becoming very hot, which, as it consists 
of 18 inches of fire-brick, shows either that the inner tempera¬ 
ture is much too high, or that the bricks have already been 
thinned by burning. 

A glance into the tuyere opening shows that a heavy black 
nose has already formed, resulting from the fusion of the fire¬ 
brick above, which form a crust almost impervious to a steel bar, 
and exceedingly infusible. 

A consultation with the man who feeds that end of the fur¬ 
nace will elicit the information that that portion of the charge is 
sinking very slowly, and that the heat is rising to the surface. 

At the same time, the blast-gauge will show an increased ten¬ 
sion, owing to the blocking up of the tuyeres that supply that 
portion of the apparatus, and the agglomeration of the charge 
above, owing to the rapidly ascending temperature. 

The already too siliceous slag is rendered still more infusible 
by the admixture of silicate of alumina from the melting fire¬ 
brick ; and the high temperature and powerful reducing atmos¬ 
phere, resulting from the almost stationary condition of this por¬ 
tion of the charge, soon begin to reduce metallic iron out of the 
slag, and even from the matte, the sulphur being driven away 
to a considerable extent by the powerful blast, high temperature, 
and slow removal of the molten products. 

The slimy, half-fused metallic iron is soon recognized by the 
bar which is constantly thrust into the choked tuyeres, and the 
inexperienced metallurgist, following the teaching of all our best 
text-books, reasons that the reduction of iron comes from too 
highly ferruginous a charge, and destroys all hope of improve¬ 
ment by cutting off a portion of the iron from the charge fed 
into that end of the furnace. 


238 MODERN AMERICAN METHODS OF COPPER SMELTING. 


This further diminution of the oxide of iron, and consequent 
necessary increase of temperature to melt the more and more in¬ 
fusible slag, soon bring about the exact conditions prevailing in 
an iron-ore blast-furnace. Metallic iron is reduced in large 
quantities, while the temperature is raised several hundred de¬ 
grees, before the slag—now virtually an acid silicate of alumina 
and lime—will become sufficiently softened to run at all. In the 
meantime, the furnace wall, at the panel, is burned nearly 
through; jets of blue flame appear at every joint and crevice, and 
the most superficial examination shows that the process is ex¬ 
tending into one or the other of the corner columns, threatening 
the stability of the structure, and still more alarming the person 
in charge. The column of ore in that end of the furnace hardly 
sinks at all; the heat is ascending to the surface of the charge; 
and the general increased stickiness of the rapidly lessening slag- 
stream, increase in tenor of the matte, and deposition of lumps 
of metallic iron in one or both compartments of the fore-hearth,, 
show that the end is not far off, and unfold the near prospect 
of a chilled furnace, and the probable presence of a block of 
half-molten ore and iron that is almost impervious to tools, and 
may result in the entire abandonment and destruction of the 
furnace. 

This is one of the most common and well-known occurrences 
in small furnaces and with inexperienced metallurgists, and 
might just as well happen to the large furnaces now under dis¬ 
cussion, were it not fortunately that their construction and man¬ 
agement are not likely to be undertaken except by men of experi¬ 
ence, and also that, owing to their greater size, a threatening— 
or even established—chill is much more easily managed than 
in the case of the smaller cupolas, whose contracted shaft is 
filled up solid almost before one is aware that anything is going 
wrong. 

Owing to the great area of the Orford furnace, a considerable 
portion of the shaft may be completely blocked by a chill, while 
a brisk fusion is progressing in the other half, giving an oppor¬ 
tunity, by the use of skill and experience, to gradually smelt 
away the solidified portion and eventually bring matters back to 
their normal condition. 

Returning to the imaginary case that has just been followed 
to a disastrous termination, the writer will endeavor to show how 



BLAST-FURNACES CONSTRUCTED OF BRICK. 


239 


such a catastrophe may he averted, and will describe the course 
of events as they have occurred scores of times to every practical 
smelter. 

The moment that it is noticed that one end or corner of the 
furnace is becoming abnormally hot, and that the column of ore 
corresponding thereto is sinking slowly, the tuyeres belonging to 
that portion of the shaft—from one to three in number—are im¬ 
mediately removed, and the openings slightly plugged with clay. 
At the same time, several charges of the most fusible slag—that 
from matte concentration and containing a very high percentage 
of iron is best—are given, in place of ore, and the whole furnace 
is most carefully watched, to learn whether the burning is due 
merely to some local irregularity in feeding, or whether some im¬ 
portant point affecting the whole process is at fault; such as too 
much or too little fuel in proportion to ore; improper composi¬ 
tion of slag; incorrect feeding; too strong or too weak a blast, 
etc., etc. 

Experience alone can qualify the metallurgist to quickly and 
correctly detect the cause of the trouble and apply the appropri¬ 
ate remedy; but in any case, if, after taking the precautions 
enumerated and waiting a sufficient time to get their full effect, 
the burning still continues, it becomes evident that the trouble is 
deep-seated and of some extent. 

Vigorous measures are therefore required to stop the melting 
of the brick-work above the tuyeres, and not only to cool down 
the heated end of the furnace, but also to repair, as far as possi¬ 
ble, the damage already done to the panels—or even to the cor¬ 
ners of the main columns. 

Still keeping the offending tuyeres closed as already de¬ 
scribed, a full charge of siliceous ore should be fed in such a way 
that it will sink to the indicated spot. This may be given either 
with or without coke, or may be followed by a second or third, 
or even a greater amount, as the circumstances indicate; proceed¬ 
ing with extreme caution, and allowing some two hours to inter¬ 
vene between charges. 

The author has found it necessary to charge as much as 11 
tons of almost pure silica—quartz with specks and veinlets of car¬ 
bonates and oxides of copper—into one corner of an overheated 
furnace, and this entirely without coke, before the gradual cool¬ 
ing of the external walls, normal and even sinking of the charge. 


240 MODERN AMERICAN METHODS OF COPPER SMELTING. 


and lowering of the temperature at the charging-door, indicated 
that the mischief had ceased. 

The office of this siliceous addition is not to render the slag 
in general more siliceous. This would only bring about the evils 
already indicated, and probably cause a heavy reduction of me¬ 


tallic iron. Its object is rather to produce, by the sudden arrival 
of such a body of cold, infusible material, such an overwhelming 
effect as completely to cool down that portion of the shaft, the 
silica itself softening somewhat and remaining for the most part 
in the corner of the furnace corresponding to the point over which 
it was charged. It attaches itself to the walls and bottom, and 
fills up the cavity caused by the fusion of the fire-brick, lowering 
the temperature at the same time to a considerable extent, but 
producing no marked effect on the general character of the slag. 

When this operation is successful, as is usually the case, the 
thinned and heated brick-work is virtually restored, the deeply 
excavated bottom is filled up to the general level, and matters 
resume their normal condition, all irregular bunches and protu¬ 
berances of the siliceous addition that inav have adhered to the 

«/ 

furnace walls becoming gradually melted away and smoothed 
down until the interior mason-work, if visible, would be seen to 
have almost assumed its original appearance*. 

Such a result may seem very doubtful, and, in fact, the whole 
operation may appear to partake too much of the marvelous to 
those unfamiliar with such practice. The author would hesitate 
before describing the foregoing operation as a matter of general 
every-day occurrence, were it not that it can be vouched for in 
its entirety by a considerable number of well-known and reliable 
gentlemen. This practice, as initiated by certain members of the 
Orford Company, already mentioned, has spread until it is now 
a well-known and recognized part of our local copper metallurgy. 
The skill attained by certain foremen in managing these very 
large furnaces is quite remarkable, and far beyond anything de¬ 
scribed in this treatise. 

While the imaginary case just described in detail represents 
only one of the various accidents peculiar to all forms of blast¬ 
furnace, it still is at the bottom of a very large proportion of 
the instances of “ freezing,” “ choking-up,” “ burning-out,” etc., 
etc. Paradoxical as it may appear, the two common accidents of 
w burning-out ” and “ freezing-up ” are closely connected, and in 


BLAST-FURNACES CONSTRUCTED OF BRICK. 


241 


reality only two different stages of the same morbid process. 
The young metallurgist cannot overestimate the importance of 
the fact that it is quartz in one or another of its forms that is 
the most frequent cause of smelting difficulties and disasters. 
Seven out of the last eight cases of metallurgical difficulties for 
which the writer was called upon to prescribe, were due to this 
cause. 

In spite of the frequency and apparent simplicity of this diffi¬ 
culty, some smelters of experience never seem to have learned 
the cause, and attribute the slow and irregular running of the 
cupola and the frequent filling up of the crucible with sows to 
“too much iron in the charge”—“too much sulphur”—“magne¬ 
sia in the limestone flux,” etc., when, in almost every instance, a 
mere ocular examination of the slag is sufficient to show that 
silica is at the bottom of the trouble. No apology is needed for 
emphasizing this point, when men considered as expert metallur¬ 
gists are constantly falling into this error. 

It is especially during such accidents and irregularities that 
the great advantages of these very large furnaces become fully 
apparent. Where a small shaft would soon be completely and 
irretrievably choked, necessitating the great expense of blowing 
down and subsequently chiseling out the half-fused mass of ore 
and cinder, no large furnace, in any instance known to the 
author, has ever become so blocked up and filled with a chill that 
it has not been quite easy to save it by using appropriate means. 
Even though one end be completely blocked, there is always 
ample space at some points of its eleven-foot shaft to permit the 
descent of the charge and retain a sufficient number of tuyeres 
intact to gradually melt out the chill and restore the shaft to some¬ 
thing like its former dimensions. Some considerable irregular¬ 
ity of form naturally results from repeated manipulations of this 
kind; but so long as sufficient area remains at the tuyere level, 
and no projecting masses impede the regular descent of the 
charge, no diminution of capacity need follow, nor increase of 
difficulty in managing the furnace. 

The accompanying sketch gives a tolerably correct view of 
the shape of one of these large brick furnaces at the tuyeres upon 
its blowing out for repairs after a continuous campaign of 8^ 
months, during which time over 18,000 tons of exceedingly fer¬ 
ruginous ore were smelted in it, yielding a very low-grade matte 


242 MODERN AMERICAN METHODS OF COPPER SMELTING. 

and a slag averaging about 22 per cent, silica and over 70 per 
cent, protoxide of iron. As it is drawn to a scale, the extent of 



THE RECTANGLE SHOWS THE SHAPE BEFORE THE CAMPAIGN ; THE 
IRREGULAR LINE, AFTER THE CAMPAIGN. 


the irregularity is easily appreciable, the original dimensions be¬ 
ing 3 feet 3 inches by 11 feet 4 inches. 

In fact, the full capacity of this type of furnace, when smelt¬ 
ing a basic ore, is not reached until the walls are burned out to 
a considerable extent, which may indicate the policy of widening 
the furnace in the first place. When smelting a siliceous ore, or 
when a large proportion of fines is present, the gain in width is 
accompanied with a decrease of temperature and irregularities in 
the descent of the charge—circumstances that soon rectify the 
trouble by adhering to the walls, and filling up the shaft again 
’with a rapidity that may be disastrous if not observed and 
remedied in time. 

As has been already briefly mentioned, the cutting down of 
the bottom and piercing of the foundation-walls is an accident 
that sometimes occurs, although usually only when the charge 
consists of a very fusible unroasted ore, producing a matte of low 
grade—from 25 per cent, downward—whose fiery and corrosive 
qualities are well known to all furnace-men. It is to the great 
quantity, as well as corrosive quality, of this substance, and this 
usually in connection with a basic slag, that this destructive pro¬ 
cess is due; and in spite of much care and expense bestowed on 
the matter, no material has yet been found that will withstand 
a daily production of from 20 to 45 tons of this intractable prod¬ 
uct. But a means of greatly lessening its destructive action, as 
well as of greatly prolonging the life of the entire structure and 
rendering its management much easier, has been discovered and 
quite generally adopted, being first brought into notice by Mr. 







BLAST-FURNACES CONSTRUCTED OF BRICK. 


243 


John Thomson, of the Orford Company. It consists in duplicat¬ 
ing* the furnace plant and running* each individual cupola only 
ten or twelve hours of the twenty-four. This is a scheme that 
seldom recommends itself to one on first hearing, but, after a 
thorough trial, will be found to possess numerous important ad¬ 
vantages, while its only drawback is the increased first cost of 
the plant—a trifling consideration in comparison with the large 
interests usually at stake. 

A mere doubling of the cupola plant is sufficient to overcome 
the difficulties mentioned; but if it be desired to reap the full ad¬ 
vantages of the scheme, a corresponding increase should be made 
in the blast apparatus. This being effected, the entire smelting* 
process may be confined to the daytime, avoiding* the difficulties 
and drawbacks of night work, saving the wages of one or more 
foremen, and rendering* it possible for the manager to retain that 
complete personal oversight of the smelting* process that is unat¬ 
tainable when half of it is concealed from his inspection. If this 
were the only benefit derived from the above plan, it would in 
most cases be well worthy of adoption; but the advantages ac¬ 
cruing to the furnaces themselves, as Avell as to the entire process, 
are too numerous and far-reaching to be thoroughly explained in 
this treatise. 

In the first place, the cutting down of the furnace bottom is 
usually completely remedied by the long and ever-recurring pe¬ 
riods of complete repose, during* which the thinned brick-work is 
again sealed by the chilling* of the molten products; the hearth 
is renewed by the solidification of the matte and slag still remain¬ 
ing in the cavities of the hearth; the overheated brick-work cools 
from the outside to such an extent that the area that to-day has 
given constant annoyance by its obstinate burning, with the con¬ 
stant threat of finally breaking through and causing serious 
trouble, will to-morrow be found as cool as, or cooler than, any 
other portion, owing to the thinness of its walls; and various 
slight difficulties that are pretty sure to occur in the course of a 
long run are averted before they become of importance, while 
the trouble begins at a new point, only to be again averted be¬ 
fore it has gained serious headway. This is by no means an un¬ 
common or imaginary case, but a matter of frequent occurrence, 
and these lines are written after several years’ trial'of both the 
■constant and intermittent method of smelting; the experience of 


244 MODERN AMERICAN METHODS OF COPPER SMELTING. 

others who have fairly tried this plan, in connection with large 
brick furnaces, being equally favorable. 

The writer’s attention was first called to this matter in 1871, 
when noticing the almost invariable improvement in behavior and 
capacity that succeeded any accidental stoppage of cupola-fur¬ 
naces that he was then managing. The ores were exceedingly 
bad and siliceous, and the difficulties detailed in the preceding 
pages followed each other with disheartening regularity and fre¬ 
quency. Great pains were taken to secure a steady and uninter¬ 
rupted run, fears being entertained that any stoppage would be 
disastrous to the furnace in the more or less critical condition 
that seemed to be its normal state j but after finding that the 
benefits following any temporary stoppage of the machinery had 
become so obvious that the foreman was in the habit of pur¬ 
posely causing slight accidents in order to help his furnace out 
of some particularly critical situation, it was decided to adopt the 
practice of stopping for two or three hours whenever the ordi¬ 
nary incidents of burning out, etc., became unusually critical. 
This habit was carried farther and farther, proceeding with 
caution and gradually lengthening the stoppages, until it came 
to be considered an almost universal remedy, and was as often 
applied for chilling or freezing up as for the opposite condition 
of affairs, and no misfortune ever arose from its reasonable ap¬ 
plication. 

This practice, like every other, must be used with care and 
judgment, and may easily be carried to an extreme, but as a rule 
is the least dangerous measure that can be adopted with a badly 
acting furnace of large area. A small furnace might easily chill 
in a few hours, so that the length of the period of repose must be 
proportioned to the size of the shaft and to the cubic contents of 
the heated material. The thickness of the walls must also be 
considered, as the rapidity of the escape of heat depends upon the 
thickness of the brick-work. It is hardly necessary to say that 
every orifice and crevice about the furnace must be tightly 
sealed, the tuyeres being removed, and their openings, as well as 
the slag-run, being tightly filled with damp clay, while the brick¬ 
work in their vicinity must be searched for possible cracks, and 
all such openings carefully plastered over. Otherwise, the incom¬ 
ing currents of air would gradually burn away all the fuel con¬ 
tained in the charge, leaving the furnace in a hopeless condition. 


BLAST-FURNACES CONSTRUCTED OF BRICK. 


245 


If it is to stand still any length of time, such as over night, a few 
extra charges of coke should be given an hour or two before stop¬ 
ping, so that there may be an abundance of fuel in the bottom 
of the furnace. A small charge of basic slag shoidd also be 
given; and as soon as the blast is taken off, the basin or fore- 
liearth tapped, and all openings sealed, the surface of the charge 
should be covered with a layer of fine coke, over which is spread 
an inch or two of fine fusible ore. The slag-liole connecting the 
furnace with the fore-hearth should be thoroughly cleared out: 
the layers of chilled slag and ashes, by which the blowing through 
of the blast is prevented, removed, and the channel itself filled 
with fine charcoal or coke, well rammed in with a u stopping 
pole.” This is rendered impervious to air by an exterior plug of 
clay, and the fore-hearth, while still hot, being scraped clean of 
all half-fused masses of slag or reduced iron, and everything be¬ 
ing prepared for the morrow’s work, the cupola may be left in 
charge of an experienced watchman—preferably an old smelter. 
On the ensuing morning, a light blast is put on, and the channel 
being cleared out, slag will flow in from five to ten minutes, while 
in half an hour the furnace will be in normal condition, and in 
most cases smelting more rapidly and satisfactorily than when 
left the previous evening. 

The extreme length of time that a large furnace may stand in 
this way without injury is unknown to the author. Much de¬ 
pends on the fusibility of the charge, the character of the fuel, 
the more or less perfect exclusion of all air, and probably also 
upon the quality and amount of sulphide compounds present, 
whose gradual oxidation may sustain the vitality of the charge 
for a much greater length of time than if absent. The following 
instances, from personal experience, show that a considerable de¬ 
lay is permissible. 

A furnace running on a fusible charge of calcined pyritic ore 
was shut down Friday noon, on account of an accident to the en¬ 
gine. Further examination showed the accident to be of such a 
nature as to cause a delay until the succeeding Wednesday night 
—-5J days—at the end of which time, a light blast was applied 
without much hope of a favorable result, although the coke on 
top of the charge was hot and glowing. 

There seemed a good deal of obstruction to the blast at first; 
but in twenty minutes, a cold, thick slag began to run, which 


246 MODERN AMERICAN METHODS OF COPPER SMELTING. 


gradually improved, until the furnace resumed its normal con¬ 
dition and capacity in about eight hours. The charge had sunk 
about two feet in the furnace during this period of repose. The 
grade of the first tap of matte (the siphon-tap being impracti¬ 
cable in this condition of affairs) was 46 per cent., the ordinary 
average being from 28 to 29 per cent. The succeeding tappings 
gradually decreased—going successively 42, 37, and 34 per cent., 
the normal grade being reached soon after the furnace had 


regained its usual capacity. 

Periods of 4 days, 3f, 3J, 3, and of less time, appear in the 
writer’s notes, the only serious accident, occurring during one of 
the shorter periods, being caused by the falling out of two of the 
tuyere-plugs, whereby a current of air entered the furnace for 
twelve hours before being discovered. The coke was completely 
burned out of the lower portion of the charge for about two-thirds 
of that part of the shaft nearest the opening; but the furnace was 
eventually saved by blowing lightly into three tuyeres at the op¬ 
posite end, which were still supplied with fuel, and little by little 
smelting out the entire half-fused block of charge. Much benefit 
was derived by introducing coke into the furnace through such 
tuyeres as seemed to warrant the trouble. Owing to the great 
size of the tuyere openings (6 inches), this was easily effected, and 
the smelting much facilitated. In fact, if any cavity in the semi- 
fused mass could have been found at any point accessible to the 
blast, nothing would have been simpler than to break a hole 
through one of the brick panels and fill the opening with coke. 
The author has done this in later instances with very satisfactory 
results, a cavity opposite the tuyeres having been formed by 
dragging out a lot of the stock, from which the coke had burned 
so gradually as not to fuse it. 

Space is wanting for a description of the use of petroleum, 
gas, and other concentrated fuels for similar purposes, as the 
writer’s own experience with such measures has been entirely un- 
satisfactory, nor can he find any record of successful cases in 
the annals of American copper smelting. 

The most Herculean efforts are warrantable when any reason- 
able probability exists of the saving of an iron furnace from com¬ 
plete chilling up ; but in copper smelting, the comparative cheap¬ 
ness and simplicity of the structure itself, and the certainty of 
being able to remove the worst chill by mechanical means in a 


BLAST-FURNACES CONSTRUCTED OF BRICK. 


247 


comparatively short time, render such unusual and expensive 
measures less important. 

The oxidation of the sulphides in the charge during the period 
of repose is an element of some importance, although seldom so 
striking as in the case just mentioned. Still, the closing down 
of the cupola over night is invariably accompanied with a per¬ 
ceptible rise in the grade of the matte produced during a certain 
period succeeding; being greatest at first, and gradually dimin¬ 
ishing as the contents of the furnace are replaced with fresh ore. 
This increase in richness is at first seldom less than 5 per cent., 
diminishing rapidly, however, as the ore nearest the bottom of 
the charge seems to have experienced the most thorough oxida¬ 
tion. 

Though apparently a trivial matter, this enrichment of the 
matte is a direct pecuniary gain, and, according to a rough esti¬ 
mate, will offset the interest on the capital necessary for the 
double plant several times over in the course of a year. 

Another useful and frequently applied remedy for various 
irregularities in cupola smelting is the so-called “ running-down ” 
of the furnace, by which is meant a mere cessation of charging 
until the column of ore and fuel has sunk to a point far below 
its normal limits. The shaft is then rapidly filled with the usual 
alternate charges of ore and fuel, and everything goes on as be¬ 
fore. 

Without attempting to explain the reason therefor, it is cer¬ 
tain that this practice is sometimes of great advantage, obstinate 
irregularities often being conquered thereby, and the normal 
condition of things resumed. It is especially useful when it is 
desired to create a sudden and profound lowering of tempera¬ 
ture at some point where a serious localized burning is taking 
place; for the exposure of the naked inclosing walls of the shaft 
renders it possible to deposit the batch of ore that is used to cool 
the walls in the exact spot w r here it is needed; and it is possible 
to use for this purpose, under such circumstances, an easily fusi¬ 
ble ore or slag, instead of the highly siliceous material that is 
usually selected when this process of cooling down is undertaken 
blindly from above. 

Wall accretions may also be reached in this manner, the 
charge being allowed to settle until they are exposed, wdiereupon 
they may be removed by a long bent steel bar introduced through 


248 MODERN AMERICAN METHODS OF COPPER SMELTING. 


one of the charging-doors, the glowing interior being cooled 
down, if necessary, by sprinkling with water. 

Still another means of remedying the cntting-down of the 
furnace bottom has been mentioned in a former section, but is 
sometimes useful in connection with the large brick furnace. 
This is the introduction, through the tuyere openings, of ore or 
sand, which, being both cold and the latter infusible, will not com¬ 
bine with the slag, as it is already below the smelting zone; but 
will simply remain in place and assist in building up a new bot¬ 
tom. By this means, even the molten masses present may be 
partially sol hi i fieri and a great advantage gained in a short time. 
The author has occasionally tried the introduction of water in 
the same manner and for the same purpose, taking as a guide the 
very decided local chilling produced by a leaky water-jacket; but 
the results, though locally satisfactory, are not sufficiently ex¬ 
tended, while the operation itself, especially in connection with a 
low-grade copper matte, cannot be recommended to any who ob¬ 
ject to certain and frequent explosions of considerable force. 

In connection with the measures already detailed for keeping 
the furnace in proper condition, may be mentioned the external 
repairs that it is feasible to execute while the furnace is still in 
blast. Not all smelters are aware of the very extensive repairs 
that may be carried out without stopping the blast more than a 
few hours; the length of the campaign often being doubled by 
the construction of a new panel, the repairing of a pillar, and 
other familiar and inexpensive operations. These are of too ex¬ 
tensive and varied a nature to be enumerated in detail; but a few 
of the teachings of experience will throw some light on the prac¬ 
tice in general. 

The replacement of one or more panels that have become so 
thin as to threaten a constant breaking through of the charge is 
a simple, though very hot and laborious, task. 

All needful material for the renewal being prepared and col¬ 
lected on one spot, the blast is shut off, the fore-hearth tapped, 
and the condemned brick-work at once broken in with sledge 
and bar. So much of the glowing charge as is necessary is at 
once dragged out of the opening with long hoes and rakes, and 
sprinkled with water so that the men can stand on it to work. 

When the bricks have been removed to the extent deemed 
necessary, the cavity left in the column of stock is quickly filled 


BLAST-FURNACES CONSTRUCTED OF BRICK. 


249 


with dampened coke, a few wooden slats being wedged across 
the opening, to keep the fuel from falling out. 

The most important measure is to obtain a solid foundation 
for the new wall, and to accomplish this, all accretions of slag 
and metal of which the old wall largely consisted, must be chiseled 
away until sound brick-work is reached, which being leveled with 
thick fire-clay, offers a proper starting-point. The work must 
proceed with great rapidity, as the passage of air through the 
opening will soon consume the fuel in the charge. Little atten¬ 
tion is paid to neatness, or even regularity, so long as strength 
and tightness are obtained. If the work promises to occupy 
more than two or three hours, the opening should be closed at 
the beginning by a thin plate of sheet-iron tightly cemented at the 
edges with clay, outside of which the new wall is raised. When 
all is completed, the sheet-iron—unless already consumed—is cut 
away opposite the tuyere openings, and the blast is put on at 
once, there being no necessity of waiting for the work to dry, as 
the heat from the furnace will evaporate all moisture quite as 
soon as is desirable. 

By this means, extensive repairs may be executed on any 
portion of the furnace, it being even possi ble to put in a new bot¬ 
tom or repair the foundation walls, by suspending the charge on 
bars driven transversely through the furnace. When possible, 
the ashes of the rapidly consumed fuel should be cleared out be¬ 
fore starting again; but there are but few instances where it will 
not be found better to blow out the furnace when such radical 
repairs are required. 

The water-jacket furnace may also be allowed to stand idle 
much longer than is usually supposed, as the absence of air pre¬ 
vents the combustion of the fuel; but the rapid conduction of 
heat through its cold metallic walls prevents any such liberties 
as may be taken with the brick furnace, and renders it unsafe to 
leave the furnace more than twelve hours.* 

In fact, it is better to run the charge down to the very bot¬ 
tom, throw in a few baskets of coke, and after stopping all the 
air-holes, leave the jacket in this condition, by which all danger 


* Since writing this paragraph, experience has taught me that water- 
jackets can be allowed to stand over night with as good results as in the 
case of brick furnaces, by employing the same precautions. 



250 MODERN AMERICAN METHODS OF COPPER SMELTING. 


of chilling is avoided, and the bottom being kept hot, smelting 
may be resumed in a very short time. 

The final blowing out of the large furnace presents no pe¬ 
culiar features. The blast should be lessened as the charge sinks, 
and as soon as slag stops running, the breast-wall, and, if expen¬ 
sive repairs are imminent, some of the rear and end panels, should 
be knocked in, and all stock and fuel dragged out, until a toler¬ 
ably even bottom is reached, which needs no preparation for the 
succeeding campaign. 

Any burning out of the brick pillars that form the main sup¬ 
port of this furnace, should be carefully watched and repaired be¬ 
fore it has proceeded to a dangerous extent. This burning is 
sometimes so obstinate that when it is important not to stop the 
furnace or blow out, it is necessary to support the superincum¬ 
bent brick-work with props and braces, which should remain m 
place until the pillars have been restored to their former strength. 

Estimates of the cost of both building and running one of 
these large brick furnaces of the Orford type will be found in 
this chapter. 

Similar estimates for the small brick furnaces formerly used 
at Ely, Ducktown, Ore Knob, and elsewhere, do not come 
within the scope of this work, which treats of modern rather 
than of historical methods. The cost of smelting in the small 
furnaces was from three to six times as great as in those now 
in use. 

There remains to be still considered the application of water 
tuyeres and other cooling devices to furnaces constructed of brick 
or stone. 

The author’s own experience is entirely in favor of the em¬ 
ployment of properly constructed iron, or better, bronze or cop¬ 
per tuyeres, containing a space for the introduction of water. In 
Colorado and other places, he has used water tuyeres with invari¬ 
able satisfaction, the only drawback being the frequent cracking 
of the cast-iron, which is now overcome. 

While they offer little or no protection to the furnace wall, 
they are indestructible themselves, and by delivering the wind at 
a fixed point, even though the walls may be eaten away all about 
them to the depth of a foot or more, they remove the point of 
greatest heat from the wall itself and practically retain the smelt¬ 
ing area at the same invariable size, the latter being practically 


BLAST-FURNACES CONSTRUCTED OF BRICK. 


251 


bounded by vertical planes passing through the nozzles of the 
tuyeres. 

It is also possible, if desirable, to project them into the interior 
of the furnace to a distance of several inches from the walls. 
Although this practically diminishes the size of the smelting 
area, it saves the walls from burning, and in case of a weak blast 
or of an unusually dense charge arising from a large proportion 
of fine ore, may render practicable the smelting of material that 
would lie impossible under other circumstances. 

They were tried on the first large Orford furnaces, but failed, 
owing to the severity of the winter and other accidental causes, 
rather than from any fault due to the tuyeres themselves. Their 
construction and management are too familiar to require further 
explanation in these pages. 

The surface cooling of the brick-work by means of a spray of 
water on the outside lias been tried on many occasions and with 
various forms of apparatus. It has rarely given satisfaction, and 
in the writer’s opinion is as dangerous and worthless a device as 
can well be imagined. 

To those familiar with the results of contact between water 
and molten matte, it is not necessary to bring up any further ar¬ 
guments to condemn a device that can only be accompanied by a 
constant wetting of everything in the vicinity of the furnace. 

Besides, the idea itself is an extremely faulty one, as, owing to 
the non-conductivity of fire-brick, a wall less than a foot thick 
may continue melting on one side, while its other surface is con¬ 
stantly sprayed with cold water. 

All devices of this kind, in which the water comes in contact 
with the free exterior surface of the furnace wall, are, in the 
author’s opinion, worse than useless, and likely to be accom¬ 
panied by most dangerous results. 

ESTIMATE OF COST OF LARGE BRICK BLAST-FURNACE. 

Excavation for foundation: 1,000 cubic feet at 8 cents $80.00 


Foundation of beton. 65.00 

Cubic feet. 

Total fire-brick for furnace proper.1,640 

Lining for cross-flue and down-take. 540 

Fore-hearth, etc. 45 


Total.2,225 

Carried forward. $145.00 









MODERN AMERICAN METHODS OF COPPER SMELTING. 


9^9 


Brought forward. $145.00 

At 18 brick per cubic foot = 40,050 at $40 a thousand 1,602.00 

Red brick for down-take and flue : 16,800 at $8. 134.40 

6| tons fire-clay at $8.. 52.00 

6 casks lime at $1.50. 9.00 

2 tons sand at $1.50. 3.00 

Old rails for binders: 180 yards at 80 pounds a yard = 

14,400 pounds at f cent. 108.00' 

Tie-rods for furnace, flue, and down-take : 620 Pounds. 

feet of 1$ iron = 2,480 pounds. 2,480 

Loops, nuts, etc. ; . 166 

Angle iron for down-take. 172 

Wrought-iron rods, etc., about fore-hearth. 66 


Total. 2,884 

At 2 cents a pound... 

Castings: Pounds. 

3 feed-door frames. 792 

Damper and frame. 455 

Plates for fore-hearth. 560 

Slag and matte-spouts. 80 

Plates for charging-floor. 1,260 

Miscellaneous. 420 


57.68 


Total. 3,567 

At 2 \ cents a pound. 

Material and labor for arch patterns and other carpen¬ 
ter work... 

Labor: 

Mason, 88 days at $4. 

Ordinary labor, 102 days at $1.50. 

9-| days, smith and helper. 

Blast-pipe and tuyeres. 

Cloth for tuyere bags and labor. 

Superintendence. 

Miscellaneous. 

Grand total. 

Tools essential to furnace, steel, and iron bars, shovels, 

rakes, hammers... 

15 slag-pots at $13.50. 

4 iron barrows at $9. 

Manometer. 

Total. 


89. 

.17 

32. 

,40 

352 

.00 

153. 

.00 

47. 

50 

136, 

.00 

3. 

.80 

120 

.00 

65, 

.00 

$3,109, 

.95 

$55, 

.90 

202. 

,50 

36 

.00 

2 

.50 

$296 

.90 


The above estimate is exclusive of main blast-pipe, blower, 
motive power, hoist, and chimney or dust-chambers; the allow¬ 
ance for cross-hue and down-take being; sufficient to cover cost 









































BLAST-FURNACES CONSTRUCTED OF BRICK. 


253 


of chimney in those exceptional cases where no provision is made 
for catching the immense amount of flue-dust generated in this 
method of smelting. 

A compact and economical hoist and ample provision for a 
large charging-floor and generous bin room are essential to con¬ 
venient and economical work. 

ESTIMATE OF COSTS OF CUPOLA SMELTING. 

Details of expense of running a 42-incli circular water-jacket 
cupola, smelting 56 tons of fusible ore per 24 hours.* 

As it may be a matter of interest to many to compare the 
cost of copper smelting in Arizona, Montana, and other remote 
districts with the cheaper scale of prices assumed for our stand¬ 
ard, this information is given in a second column. These figures 
refer to works situated near a line of railroad, and of large ca¬ 
pacity, as the smelters at a distance from travel must frequently 
pay double or even treble the amount given for coke and other 
supplies, while the cost of running a single furnace is propor¬ 
tionately much greater. 

PER TWENTY-FOUR HOURS. 


Fuel and supplies. East. Arizona. 

Eight tons coke. $40.00 $200.00 

Fuel for Blast and attendance. 7.50 16.00 

Clay and sand. .60 1.50 

Five tons limestone (or other flux). 7.50 15.00 

Cost of pumping water for jacket. 4.80 11.50 

Oil, lights, etc. 3.50 9.00 

Renewal of tools, pots, molds, etc. 2.25 4.60 

Repairs on furnace and machinery. 2.00 4.10 

Proportion of cost of blowing-in and out. .40 .85 

Sinking fund to replace furnace, etc. 1.65 2.95 

Miscellaneous. 4.00 11.00 


$74.20 $276.50 


* These estimates, both of construction and smelting, are taken from the 
results of actual work, not being drawn exclusively from any one establish¬ 
ment, but being the average results of several successful works represent¬ 
ing advanced American practice. 

It must not be forgotten that several of the heaviest items that go to 
make up the running expenses of all metallurgical establishments are nec¬ 
essarily omitted. These are the general expenses and salaries; extraordi¬ 
nary expenses arising from accidents; cost of experimental work, and 
similar matters, which may aggregate a very large amount. 


» 


















254 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Labor (per twenty-four hours). East. Arizona. 

Six men on lower floor. $10.00 $15.00 

Four men on charging-floor. E00 13.00 

Two foremen. 5.00 10.00 

Two laborers. 3.00 6.00 

Proportion of blacksmith work. 1*25 3.50 

Proportion of laboratory work. 2.00 7.00 

Proportion of superintendence. 3.20 10.50 


$31.45 $65.00 

Fuel and supplies. 74.20 276.50 


Total. $105.65 $341.50 

Costing respectively per ton. $1.88^ $6.10 

To which should be added 5 per cent, for resmelting foul slag 
and flue-dust, increasing the final cost to $1.98 and $6.40 a ton. 
Nothing is allowed for transporting ore to the furnace and many 
other items, which only obscure an estimate supposed to refer to 
the cost of running a furnace as part of a larger plant. 

If the entire expense of the works were supported by a single 
smelting-furnace, the estimate would be so complicated and the 
cost of smelting so high as to create an entirely false impression. 
Such instances occur, however, though only financially successful 
under exceptionally favorable conditions and with abundant and 
high-grade ores. 

The following estimate of the cost of smelting a fusible ore in 
the large brick furnace so often referred to is also based upon 
the same conditions, the furnace being supposed to be only a 
portion of a large plant, and only to be charged with its own 
share of the cost of power, superintendence, etc., etc. 

The ore is supposed to be a low-grade, roasted pyrites, or 
some other equally fusible and self-fluxing material. It is as¬ 
sumed that the furnace makes campaigns of nine months, smelt¬ 
ing daily 95 tons of ore. 


ESTIMATE. 

Fuel and supplies: 

12£ tons coke, at $5. $61.67 

Four tons pea coal for blower, at $3.50. 14.00 

Sand and clay. 2.45 

Oil, lights, etc. 4.40 

"Wear and repairs on slag and matte-pots. 3.85 

"Wear and repairs on other tools. 1.12 


Carried forward 


$87.49 
























BLAST-FURNACES CONSTRUCTED OF BRICK. 


255 


Brought forward. 

Daily slight repairs on furnace. 

Proportion of radical repairs at close of campaign (found 

by experience to be 3 cents a ton). 

Wear on belting, blower, etc. 

Engine and boiler. 

Proportion of cost of blowing in and out. 

Sinking fund. 

Miscellaneous. 

Labor (per twenty-four hours): 

Six men below at furnace. 

Four feeders. 

Six wheelers. 

Two metal men. 

Two laborers. 

One dump man. 

Two foremen. 

One engineer. 

Blacksmith work. 

Laboratory work. 

Superintendence. 


$87.49 


2.60 


2.85 

1.25 

1.45 

.72 

1.95 

6.50 

10.00 

8.00 

9.00 

4.00 

3.00 

2.00 

5.00 

2.50 
2.10 
2.00 
4.00 


Total. $156.41 

Or a cost per ton of. $1.64f 


Adding 8 per cent, for resmelting slag and flue-dust, gives 
total cost per ton. 


$1.78 

























CHAPTER XI. 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 

The capacity of a blast-furnace is dependent upon many vary¬ 
ing causes, and is to a considerable extent independent of shape 
or size, though its tuyere area is, of course, the most important 
factor in determining the amount of material that can be passed 
through it. 

Next to the fusibility of the charge, the pressure and volume 
of the blast have the principal influence in determining this point, 
assuming always that the fuel used is of sufficient strength and 
density to permit the full pressure of wind that may be found 
most advantageous. 

Nothing can be more striking than the change in the rate of 
smelting of a large cupola-furnace as the wind pressure is dimin¬ 
ished or increased. 

The author has taken occasion during the smelting of a fusi¬ 
ble charge, and with the furnace in perfect condition, to ascer¬ 
tain the difference of capacity effected by changes in the strength 
of the blast. 

As the influence of the change is almost instantaneous, it is 
easy to arrive at such figures with considerable accuracy, meas¬ 
uring the capacity by noting the number of pots of slag pro¬ 
duced during periods of an hour each, and with varying wind 
pressure. 

The following table shows the result of these experiments in 
a compact form, repeated sufficiently often under varying con¬ 
ditions to establish their comparative accuracy. 

It should be mentioned that, in order to insure the accuracy 
of each observation independently of the condition of the fur¬ 
nace previous to the experiment, which might have been influ¬ 
enced by the preceding test, nearly all the trials were made at 
different times, but with the furnace as nearly at its normal state 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


as possible, and running under its ordinary pressure of blast— 
about 10 ounces per square inch: 


No. 

of 

test. 

Blast pies- 
snrein oz 
per sq. in. 

Production in 
tons per 24 
hours. 

Assay of slag 
in copper. 

1 ... 

X 

16>4 

0-27 

2... 

1 

21 

0'35 

3... 

2 

31^ 

0’30 

4.. 

3 

44 

0'31 

5... 

4 . 

64 

0-31 

0 ... 

6 

86 

0 5! 

7... 

8 

8714 

0-40 

8 ... 

9 

91 

042 

*9 . 

10 

9% 

0 42 

10 ... 

12 

113 


11 ... 

13 

111 


12... 

14 

116 

0-66 


Condition of furnace at close of 
experiment. 


Very hot. All tuyeres bright. 

Very hot. All tuyeres bright. 

Very hot. All tuyeres bright. 

Slag hot and smoking. Tuyeres bright. 
Slag hot and smoking. Tuyeres bright. 
Slag hot and smoking. Tuyeres bright. 
Slag still hot, but not quite so strikingly 
so as with lower pressure. Tuyeres 
satisfactory, hut beginning to form noses. 

Less hot. Decided noses. 

Much cooler. All tuyeres require opening. 


These tests, although not entirely uniform in every respect, 
are still quite regular, and agree closely with many previous ob¬ 
servations. 

With a light blast, the capacity falls rapidly, though the tem¬ 
perature rises, and the reducing action becomes more powerful, 
as evinced by the reduction of the oxidized copper in the slag, 
and the almost invariable appearance of small masses of metallic 
iron in the fore-hearth. 

With the highest available blast, 14 ounces per square inch, 
the production still increases, though only slightly above the 
normal capacity, but it is evident more wind is introduced than 
can be consumed by the fuel; a lowering of temperatime occurs, 
as distinctly shown by the appearance of the slag 5 the reducing 
action is less powerful, as seen by the slag assays; and thick, 
hard noses are formed about each wind stream, which would soon 
obstruct the blast, and probably cause a general chilling of the 
furnace. 

Thinking that some of these evils might be attributed to the 
volume rather than the pressure of the blast, the tuyere openings 
were decreased from oh to 3| inches in diameter, reducing the ca¬ 
pacity of the furnace about 10 per cent., but otherwise effecting 
no visible alteration in the phenomena described. 

Judging from this series of tests, as well as from numerous 
former trials, when smelting both lead and copper ores of many 
different varieties in cupolas of various sizes and under very 
varying conditions, it seems advisable to limit the blast pressure 


* Normal pressure and slag assay. 




















258 MODERN AMERICAN METHODS OF COPPER SMELTING. 


to the point just indicated. In no single instance lias anything 
more than a temporary increase of capacity accompanied a blast 
pressure above 12 ounces per square inch, and the rapid cooling 
of the furnace and formation of heavy and solid noses have soon 
brought the experiment to a termination. 

It seems, therefore, that a pressure of from 8 to 12 ounces, 
’with a tuyere diameter of from 4 to 54 inches, is best suited to 
the ordinary conditions of copper smelting. 

The employment of soft-wood charcoal or other fragile fuel 
may make it necessary to diminish even this light pressure, while 
anthracite may demand a more powerful blast for its most 
economical use. Information is wanting regarding the use of 
anthracite, but it is doubtful whether any advantage would be 
gained by its employment, its powerful reducing qualities causing 
an almost certain formation of sows. 

Of the employment of a heated blast for copper smelting, the 
author must plead almost complete ignorance. The few details 
that lie can gather on this subject indicate that no advantages 
commensurate with the cost of plant have been obtained by its 
adoption, and the tendency of a hot blast to increase both tem¬ 
perature and reducing action is obvious. 

The common claim urged by inventors and manufacturers of 
smelting-furnaces is, that their apparatus is capable of generat¬ 
ing a temperature much higher than ordinary furnaces. 

This shows an entirely mistaken notion of the process of 
smelting, where our constant endeavor is, to prevent the tempera¬ 
ture rising much above the point necessary for the fusion of the 
earthy constituents into a liquid and homogeneous slag. 

The method of charging is pretty nearly universal, and differs 
radically from the old practice, where the establishment and pres¬ 
ervation of a nose seemed to be the chief aim and end of the 
smelter’s labors. 

Both ore and fuel are now pretty generally spread in horizon¬ 
tal layers over the whole area of the furnace, instead of throwing 
the coke toward the center, while the charge was carefully placed 
against the walls. 

The introduction of water-jacketed cupolas and the very 
general adoption of the conical shape, whereby the gases escape 
with less velocity, and the ore is forced to descend in the neigh¬ 
borhood of the walls, have doubtless initiated this method of 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


259 


charging, which has been followed with advantage by those who 
prefer the brick furnace, and still adhere to vertical walls. This 
mode of feeding, however, should by no means be blindly adhered 
to, as nothing exerts a more powerful influence upon the running 
of the furnace or has a more important effect in keeping it in nor¬ 
mal condition than skillful and judicious feeding. 

In the brick furnace especially, the position of feeder is one 
of vital importance, and the experienced furnace foreman will 
spend a large proportion of his time on the charging platform. 

This matter has been discussed and exemplified in the section 
on large brick furnaces, and is worthy of the most careful study 
and attention. 

The absolute size of the charge to be used must vary accord¬ 
ing to local conditions. 

The most important of these are the area and height of fur¬ 
nace ; mechanical condition of ore ; nature of fuel; and extent of 
reducing action desired. 

Large and high furnaces naturally require heavier charges of 
ore and fuel; a charge made up almost entirely of coarse ma¬ 
terial may safely be fed in thicker layers than if composed prin¬ 
cipally of fine dirt, which opposes a powerful obstacle to the pas¬ 
sage of the blast; a heavy, compact coke will bear a much 
weightier charge than light, fragile fuel, like soft-wood charcoal; 
and a more thorough mixing of ore and fuel, as effected by using 
small charges, will undoubtedly bring about a more powerful re¬ 
ducing effect than when the different strata are of sufficient depth 
to retain their relative position to a considerable depth. 

While very numerous exceptions exist, the author prefers, in 
general, large charges to small ones, having found, as a rule, that 
the furnace runs more smoothly and regularly, and also that a 
slight saving in fuel is effected. 

This observation will no doubt be challenged by many com¬ 
petent metallurgists, but is the result of too long experience to 
be disproved without actual trial. 

In only one instance has the writer attempted to determine 
this point by actual experiment; but in the case referred to, the 
conditions of the trial were particularly favorable for a fair and 
impartial comparison. 

The furnace was a 42-inch water-jacket, smelting a mixture of 
reverberatory copper slag and fine unroasted pyrites, with gas 


260 MODERN AMERICAN METHODS OF COPPER SMELTING. 


coke as a fuel. The foreman, who was a most skillful smelter, 
was directed during the entire experiment to give his attention to 
the consumption of fuel, using no more than was necessary to 
attain the best possible results. The change in the size of the 
charge was made without directing his attention particularly to 
it. He was thus left to discover any necessity for a change in 
the weight of fuel. 

The experiment w r as begun with large charges—1,480 pounds 
of mixture—the relation of the fuel to the same being as 1 to 9*3. 
This was maintained for 72 hours, the furnace remaining in ex¬ 
cellent condition, and averaging 57 tons per twenty-four hours. 

The charge was then reduced to 740 pounds, just one-half of 
the original amount, and twenty-four hours were allowed to 
elapse, to permit matters to find their normal level under the new 
conditions. 

Within six hours of the substitution of the smaller charge, 
black noses began to form on the tuyeres, and the rate of smelt¬ 
ing became decidedly slower. Several empty charges—that is, 
fuel without ore—were given at intervals 5 but it became evident, 
from increasing irregularities, that the furnace was growing cold. 
A slight addition was made to the fuel charge, and after a con¬ 
siderable number of trials, the normal ratio of fuel to ore for the 
new conditions was established, and the steady run resumed. A 
three days’ average w^as taken, as in the former case, and showed 
the best possible ratio between charge and fuel to be as 8*6 to 1 . 

The charge was again halved, being now reduced to 370 
pounds, and the last-named proportion of fuel maintained until 
circumstances compelled a change. 

In brief, another three days’ observation showed a further re¬ 
duction in the ratio of ore to fuel—7’82 to 1 being the best at¬ 
tainable results. It is also interesting to note that, although 
great pains were taken to secure the same conditions in every 
particular during the entire course of the experiment, the matte 
decreased in tenor with the decrease in the weight of the charge 
—the average assay reports for the three periods of three days 
each, beginning with the heaviest charge, being respectively 46'4, 
44‘5, and 42T per cent.—the amount of the same increasing with 
its poorness in a very nearly corresponding degree. The slag 
also (although this may have been a coincidence) showed lower 
proportions of copper, assaying for the three periods respectively 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 2G1 


O'Gl, 0‘47, and 041, which is a greater difference than can he ac¬ 
counted for by the lower grade of the matte, and which in all 
probability, in common with the latter material, depended upon 
the more powerful reducing effect, due to the use of thinner 
charges, and a consequently more perfect mingling of ore and 
fuel. The capacity fell from 57 tons, in the first instance, to 51 
in the second, and down to 41 *5 in the third. 

The experience at several Arizona furnaces contradicts the 
above results, quite small charges having been found to answer 
best, although this may be due to the fact that much of the ore 
there is fine, while a powerful reducing action is necessary to pro¬ 
duce a clean slag. 

A propei* charge for a 36-inch furnace is from 500 to 800 
pounds; while a 42-inch shaft should receive from 1,200 to 1,600, 
and a 48-inch furnace, 1,800 pounds or more. The large elliptical 
slag-furnaces at the Lake Refining-Works are charged with 
about 2,600 pounds of ore and flux, experience having shown the 
advantage of deep layers in the furnace shaft. 

As may be imagined, the large Orford furnaces take still 
heavier charges, from 3,000 to 4,000 pounds being the ordinary 
standard. 

The shape of the furnace is largely a matter of individual 
preference, as may be seen by observing the almost equal num¬ 
ber of skilled advocates for the round, rectangular, and elliptical 
form. 

Beyond a certain limit, however, the rectangular form alone 
is used, owing to the feeble penetration of the light blast used in 
copper smelting. 

Experiments made by Herreslioff and other metallurgists, in¬ 
cluding the author, seem to indicate a radius of 28 inches as 
about the extreme practicable limit for a 10-ounce blast. In a 
larger furnace, while the writer has never seen any evidence of 
an untouched central core, beyond the penetration of the blast, 
the capacity increases very slowly, if at all; while the same area, 
when changed into a rectangular form, gives proportionately 
greater results. 

If the charge contains over 50 per cent, of fine ore, the figures 
given above should be considerably reduced. 

While the effects of a flaming throat are not so obviously det¬ 
rimental in copper smelting as in the fusion of the more volatile 


262 MODERN AMERICAN METHODS OF COPPER SMELTING. 

metals, it still is found by experience that such a condition of 
affairs is incompatible with the best work, being invariably indic¬ 
ative of a faulty condition of the process. 

With an open charge and long-continued high pressure of 
blast, it is almost impossible to prevent the heat from eventually 
rising, until the chimney and walls above the charging-door be¬ 
come so hot as to ignite the escaping gases instantaneously. 

The ore near the top of the charge soon sinters together j the 
fuel is largely consumed before it reaches the zone of fusion • the 
softened lumps of ore stick to the side walls, forming bulky ac- 


FRONT VIEW 




cretions, and the way is paved for the successive steps of u burn¬ 
ing out,” reduction of metallic iron, and u freezing up,” already 
so frequently alluded to. 

While it is sometimes impossible to prevent the early stage of 
this condition of affairs, when pushing the furnace to its full ca¬ 
pacity with a heavy blast, the end results should be borne in 
mind and the remedy applied in time. 

This consists simply in letting the charge sink—under a light 
blast—until the shaft is empty for a distance of three or four 
feet below the cliarging-door. One or more charges of fusible 

























































































































GENERAL REMARKS ON BLAST-FURNACE SMELTING. 263 


slag are tlien given, and the furnace rapidly filled full with its 
normal burden. In this way, the overheated walls are cooled, 
the surface of the charge regains its normal temperature, and the 
furnace under a few hours of hglit blast is again ready for a 
period of hard driving. 

In obstinate cases, the cooling of the throat with a spray of 
water is quite admissible, and often of great benefit. 

The question of the characteristics and comparative value of 
the ordinary fuels used in blast-furnace work has been discussed 
so exhaustively in most of the standard works on metallurgy as 
to render it useless to undertake any such task in a treatise like 
the present, devoted to a certain stated purpose. 

The same may be said of fire-brick - and other refractory 
materials, our own domestic brick being quite equal to any of 
foreign make for all purposes connected with blast-furnace smelt¬ 
ing. It is hardly necessary to say that, among the numerous 
competing varieties of fire-brick, only those should be selected 
which long and thorough trial has shown to be suited to the pur¬ 
pose ; the first cost should have but slight weight hi the choice. 

The manipulation of the products of fusion becomes a ques¬ 
tion of considerable importance in a country where wages are 
high, and where the large scale on which most enterprises are 
conducted renders the mechanical details of the process so much 
more prominent than in the European works from which we 
drew our first patterns. 

The transportation of the slag from a furnace smelting five 
tons an hour, and where the edge of the dump advances at a rate 
of several feet a week, soon becomes a matter of considerable ex¬ 
pense. 

Aside from the removal by a current of water, mentioned in 
an earlier chapter, no advance has been made on the two-wheeled 
slag-pot, although so much difficulty has at times been experienced 
in removing the slag in this manner with sufficient rapidity as to 
necessitate the addition of a second fore-hearth and slag-run to 
the furnace, on the opposite side from the original opening. 

Little need be said regarding the slag-buggies as furnished by 
the manufacturers of metallurgical appliances, except to urge the 
necessity of extreme lightness combined with strength. The at¬ 
tachment between pot and axle is rarely sufficiently strong, and 
the axle itself should be chilled or case-hardened to prevent its 


264 MODERN AMERICAN METHODS OF COPPER SMELTING. 


rapid destruction where the wheel takes its bearing. The accom¬ 
panying cut shows the form of slag-buggy adopted by the Orford 
Company, and is the best and strongest pattern known to the 
author. 

The ordinary complement of slag-pots to a 50-ton furnace is 


10, which number should be doubled if it is expected to allow the 
slag to cool before dumping, as should always be done if possi¬ 
ble, in order that the bottom of every potful may be examined 
for shots of matte. 

Great care should be taken to maintain the dump perfectly 



smooth, which may be easily effected by pouring pots of liquid 
slag over its entire surface. The sole duty of one experienced 
workman should be to examine the slag and keep the dump in 
order, by which means a control of the smelting is maintained 
and the labor of the pot-runners greatly lessened. 

As slag-dumps are not infrequently situated on the margin of 
a river or lake, the danger of dumping entire pots of slag into 
water, when they are only partially cooled, should always be im¬ 
pressed upon the workmen. Terrific explosions sometimes result 
from the penetration of water to the liquid center of a cake of 
slag that appears quite solid on the outside. 


























































GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


265 


The writer has seen, from this cause, several men badly in- 
jured; the iron roof and siding* partially stripped from a building* 
200 feet distant, and an entire town a mile distant alarmed by 
the explosion of a cake of slag. 

BLOWERS AND ACCESSORY BLAST APPARATUS. 

All apparatus employed for the production of a blast may be 
divided into two classes : 

I. Those producing a positive blast, and which, if obstructed, 
must result in the bursting of some part of the apparatus or the 
stopping of the blower. 

II. Centrifugal fan-blowers, which, even if obstructed, con¬ 
tinue revolving, consuming much less power than when en¬ 
gaged in actual work, as the air is simply beaten by the vanes, 
and revolved in the machine itself, without passing out of the 
pipe. 

This distinction is not always clearly appreciated, and serious 
mistakes in the construction of the plant sometimes arise from a 
misunderstanding of the properties of the machine which is to 
furnish the blast. 

Such errors can always be avoided by application to a repu¬ 
table manufacturer of blowing apparatus, as the subject is one to 
which much attention has been paid by these parties, who are 
for the most part quite capable of planning and erecting a suit¬ 
able blowing plant upon a full understanding of the require¬ 
ments of the case. 

Owing to the light blast used by all copper smelters in the 
United States, the high-priced cylinder blowers, as required in 
iron-smelting plants, are seldom, if ever, adopted. 

The blowers in almost universal use are frequently styled u fan- 
blowers ” in general • but this is a misnomer; for, although it is 
true that both types of blower in common use resemble a fan in 
appearance, the results obtained are widely different; one class 
belonging to the first section, or “ positive pressure blowers,” 
while the other is truly a u centrifugal fan-blower,” and belongs 
under the second heading. 

To the positive pressure blowers belong the “ Root,” u Baker,” 
and “ McKenzie ” blowers, all of which are too well and favorably 
known to require description or recommendation. 

The volume of air delivered by one of these machines can be 


2GG MODERN AMERICAN METHODS OF COPPER SMELTING. 


calculated with great accuracy, while the pressure simply depends 


on the rapidity of revolution. 

From tlie nature of the apparatus, the wind is delivered in a 
succession of rapid but distinct impulses and puffs, to which pe¬ 
culiarity the adherents of the apparatus attach a great, although 


somewhat mysterious, virtue, while its rivals bring forward 
equally convincing proofs of its damaging effects upon the smelt¬ 
ing process. 


According to the author’s experience with the principal makes 


of domestic blast machinery, these puffs have neither a damag¬ 
ing nor beneficial effect; an unbroken stream of wind of equal 
volume and pressure producing exactly similar results. 

From the nature of the apparatus, more power must be re¬ 
quired to drive its closely fitting parts than if' they revolved 
freely in space, while the cog gearing by which motion is im¬ 
parted to the piston in most instances produces its disagreeable 
sound and adds to the number of parts subject to wear. 

But the workmanship is so excellent, and the various parts in 
the modern machines of this type are so admirably fitted and ad¬ 
justed, that the evils just mentioned are reduced to a minimum; 
wliile the nature of the blower is such that only a comparatively 
slow motion is required to produce the desired effect. 

The machines of the second class, or centrifugal fan-blowers 
proper, consist merely of a light blast-wheel revolving in an in¬ 
closure of much greater diameter, and so shaped that wind enters 
the escape-pipe largely from the centrifugal force acquired by the 
enormous velocity imparted to it by the fan. 

The smaller blowers make from 4,000 to 5,000 revolutions a 
minute, and those of even 5 or G feet in diameter are speeded up 
to 1,500 or 2,000. 

While this is an excellent device for the delivery of a large 
volume of wind, the element of pressure is only obtained by a 
great waste of power, the speed necessary to produce a given 
pressure increasing out of all proportion to the gain in that 
quality. 

The admirable workmanship of the “ Sturtevant ” and of other 
kindred fans, and the skill with which the inherent defects of this 
method of gaining pressure have been reduced to a minimum, 
have caused the adoption of this form of blower in many estab¬ 
lishments where a considerable pressure is required. 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


267 


But while the writer fully recognizes its usefulness over a very 
wide range, its fatal defects as a blower for smelting purposes 
cannot be concealed. 

A cupola, for instance, filled to the throat with fine ore and 
using for fuel a very dense variety of coke, shows evidences of 
chilling, while the tuyeres become capped with a tenacious slag, 
which requires a forced blast to keep them open. If the blast is 
derived from a positive blower, it rises to the occasion, and the 
pressure of the wind keeps pace with the growing obstruction, 
as may be seen by observing the gauge. More work is thrown 
on the engine, and the pressure rises until the obstruction is 
cleared away, or some portion of the machinery or blast-pipe is 
overtaxed. (Positive blowers should always be provided with a 
safety-valve.) 

The result is quite different with the fan; for as the wind- 
stream is obstructed, so is the delivery lessened, until finally, with 
the complete closure of all blast openings, the work of the engine 
drops to almost nothing, and the fan revolves at its full speed, 
neither receiving nor delivering a cubic inch of blast. This may 
be easily verified by suddenly shutting the main blast-gate ‘be¬ 
tween the fan and the furnace. The unaltered stand of the ma¬ 
nometer and the sudden decrease of the labor performed by the 
motive power will sufficiently convince the most skeptical. 

With coarse ore, an easily fusible charge, and large tuyere 
openings, the lightness, compactness, and low first cost may speak 
in favor of the fan-blower for cupola work. 

The Orford Company makes use of the fan even for its enor¬ 
mous furnaces, but expends from 50 to 75 horse-power in obtain¬ 
ing a blast that, according to both theory and experience, could 
be produced with about one-third of this expenditure of force 
with the positive blower* 

Where the positive blower is used, it is an excellent arrange¬ 
ment to have engine and blower combined, thus rendering the 
blast entirely independent of the remaining plant. 

Owing to the vastly varied practice in regard to the size of 
tuyeres used, and consequently in the volume of wind required, 


* Experiments by Mr. H. M. Howe contradict this statement, as regards 
power required, but the author is not willing to accept their results in de¬ 
fiance of long years of practical observation. 




268 MODERN AMERICAN METHODS OF COPPER SMELTING. 


it is difficult to give accurate figures regarding the power required 
for a furnace of any given size. 

Elaborate tables, showing the horse-power required under 
nearly all possible conditions, are issued by the blower manufact¬ 
urers, and are in many cases quite correct, as controlled by indi¬ 
cator cards taken in the presence of the writer. 

As a guide for possible estimates, it may be assumed that eight 
horse-power will drive a positive blower suitable for a 36-inch fur¬ 
nace, while a 48-inch cupola will require from 12 to 14 liorse-power. 

The speed required by the fan-blowers is so great as to de¬ 
mand some attention to the arrangement of pulleys and shafting 
to obtain the same. 

Care should be taken to use the largest-sized pulleys practi¬ 
cable, both for driving and receiving, and all abrupt belting from 
very large to very small pulleys will always give trouble. 

A much neglected portion of the blowing-plant is the pipe 
that conveys the blast. By a strict observance of the following 
rules, much annoyance may be avoided. 

Use galvanized iron, No. 22 to 24. For any length of pipe 
up to 50 feet, make the blast-pipe 20 per cent, larger in diameter 
than the outlet of the blower; for from 100 feet to 200 feet, 30 
per cent, larger, and if the distance be over 200 feet, make the 
entire pipe 50 per cent, larger. This precaution will diminish 
friction and greatly increase the effective blast. 

If branches are used, remember that, on account of friction, 
two pipes of a given area can convey only about three-quarters 
the wind of a single pipe of their combined area. 

Make easy curves, avoiding all angles. 

All joints should be riveted and soldered. Remember that 
the slightest leak may reduce the effectiveness of the blast to an 
enormous extent. 

Have tight-fitting blast-gates in the main pipe and at each 
tuyere. 

Maintain a reliable quicksilver manometer connected with the 
wind-box surrounding the furnace, and accustom your furnace- 
men to rely upon it as the seaman relies upon the barometer. 

Remember, in this connection, however, that with a positive 
blower, a high stand of the manometer may indicate that the 
tuyeres are obstructed as well as that the blower is working satis¬ 
factorily. 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 269 


A heavy boiler-iron damper should always be fitted in the cu¬ 
pola fiue or down-take, and should be lowered to just such a 
point that the fumes escape lazily, but without issuing from the 
charging-door. By this precaution, a diminution of 90 per cent, 
in the amount of flue-dust may be effected—by accurate and long- 
Bontinued trial. 

MODERN AND ACCESSORY BLAST-FURNACE APPARATUS. 

While the slag from nearly all American copper cupolas is run 
into movable pots and thus conveyed to the dump, the more valu¬ 
able product is handled in several different ways, according to its 
richness and to local custom. 

Furnaces containing an inner crucible or an exterior fore- 
hearth, in which the metal collects in considerable quantities, and 
where no metallic copper is produced, are usually tapped into 
sand-molds, made of a slightly moistened sandy loam. With 
proper management, this method is economical and satisfactory, 
and suited to almost any grade of metal; but to avoid the untidi¬ 
ness resulting from the presence of a largo quantity of sand in the 
neighborhood of the furnace, as well as the frequent mixing of 
the same with the liquid matte from careless manipulation, a 
series of heavy cast-iron molds, communicating with each other by 
lateral projecting lips, is sometimes preferred.. It is necessary to 
warm them thoroughly just before tapping, to prevent injury 
from the enormous temperature to which they are exposed. 

The Western water-jacket furnaces are almost invariably pro¬ 
vided with two iron spouts—one in front, for slag; the other, at 
the back or side of the furnace, and several inches below the 
former, for metal. 

The slag is tapped into pots at intervals of from five to fifteen 
minutes, by piercing a clay plug with a light, pointed steel bar, 
while the metal collects until the space between the two spouts is 
filled, when it is tapped into rectangular iron molds, with taper¬ 
ing sides and ends, and mounted on wheels. The ordinary weight 
of the pigs thus produced is from 250 to 400 pounds. The 
method is convenient and cleanly, though a considerable expense 
arises from the rapid destruction of the metal molds. 

In furnaces provided with a siphon-tap, and in which the 
molten products flow continuously, the matte is usually received 
into ordinary slag-pots, and allowed to stand until it is chilled snfli- 


270 MODERN AMERICAN METHODS OF COPPER SMELTING. 

ciently to be dumped on the floor of the building. This prac¬ 
tice not only requires a large number of pots, but also leaves the 
matte in a peculiarly massive and unmanageable condition, some 
of the lower grades of metal produced from basic ores being al¬ 
most malleable from the excess of iron present. It is at times 
hardly possible to break them with a heavy sledge, and their sub • 
sequent crushing is ruinous to the machinery employed. 

On this account, the old plan of pouring the liquid matte on 
a cold iron plate is sometimes adopted, and with very satisfac¬ 
tory results. Heavy plates of cast-iron are used, 30 by 55 inches, 
and from 2 to 3 inches thick. These are inclosed by a tapering 
border, some 3 inches high; and the liquid matte, when poured 
upon them, spreads out at once into a thin sheet which is easily 
broken up into sizes suitable for immediate stall or heap-roasting, 
and in excellent condition for pulverization. 

An ingenious improvement in connection with “ tapping" 
has been introduced into the Grant Smelting Works, and other 
Colorado establishments, and although intended for furnaces 
smelting the precious metals, may be applied also to copper fur¬ 
naces where the manner of tapping is such as to call for it. 

When copper or lead matte containing the precious metals is 
tapped into an iron pot or basin, a considerable quantity of slag 
gushes out at the close of the operation. This, owing to splashes 
of metal, which have spattered over the sides of the pot to a con¬ 
siderable height, becomes so rich in silver (and gold) as to cause 
too great a loss if thrown away, while it may yet be so poor as 
scarcely to repay another fusion. To obviate this difficulty, at 
some works, the tapping-pot is provided with several plugged 
openings, at about the point corresponding with the lower sur¬ 
face of the slag which floats upon the metal. After tapping, it 
is allowed to cool for a few moments, when the lateral plug is 
pierced, and the supernatant slag flows out in a liquid state, leav¬ 
ing, however, a thin crust covering the walls of the pot, the cold 
iron having rapidly chilled the slag with which it was in contact, 
and which also contains all the metal that, was splashed against 
the basin in tapping. In this manner, a few pounds of slag are 
obtained, assaying from 12 to 15 ounces of silver to the ton, in 
place of some hundreds of pounds containing only 4 or 5 ounces, 
of the precious metal. 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


271 


MATTE SMELTING IN BLAST-FURNACES. 

To one accustomed to the smelting of copper ores in blast¬ 
furnaces, the fusion of roasted matte presents no difficulties, as 
the homogeneity and fusibility of the material, coupled with the 
absence of silica, alumina, and most other refractory substances, 
relieve the operation of its chief difficulties. 

A single examination of a proper sample of the calcined ma¬ 
terial reveals the proportion of oxide of iron—and other bases 
—present, and determines the amount of siliceous flux that must 
be added to produce a proper slag. 

As the slag resulting from the fusion of matte almost always 
contains enough copper to demand its further treatment—owing 
to the extreme richness of the product—it is usually advanta¬ 
geous to add the smallest possible proportion of siliceous flux com¬ 
patible with the formation of a reasonably pure slag. In this 
way, a slag is obtained that is so rich in iron as to be of great 
value as a basic flux in the smelting of siliceous ores. No ma¬ 
terial generally accessible to the metallurgist is more fusible or 
more useful in correcting a faulty mixture or in clearing out a 
choked furnace than the one in question. 

If carbonate or oxide ores of a siliceous nature are available, 
the entire aspect of the smelting process is changed for the bet¬ 
ter, as they can be used as a flux for the roasted matte, while, be¬ 
ing free from sulphur, their copper contents assist in producing 
a concentrated matte of higher percentage than would otherwise 
result. 

The last-mentioned benefit is so great that it is usually profit¬ 
able to purchase such ores even at a price so high as to leave no 
margin after deducting the working costs. 

Owing to the great distances between most of the establish¬ 
ments engaged in smelting sulphide ores and the mines produc¬ 
ing siliceous oxidized ores in any considerable amounts, but few 
instances occur of such a happy condition of affairs; and there¬ 
fore in most cases, gravel, pebbles, and other barren substances 
are used as a flux to the matte. 

When forced to adopt this unfortunate practice, experience 
has shown that more economical and better results are obtained 
by the employment of some acid compound—such as clay slate, 
silicate of alumina with a small proportion of other bases, etc. 


272 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


—than by using pure silica, in the shape of quartz pebbles, 
crushed quartz, sand, rock, etc. 

The extreme infusibility of the latter requires a much higher 
temperature for its combination with the protoxide of iron than 
do the less refractory substances named. A pretty thorough 
trial of almost every available material has led to a preference 
for ordinary mica-scliist or clay slate j the next best substance is 
broken common red brick, the form of the latter rendering them 
superior to the clay from which they are made. 

In all cases, the siliceous flux should be broken to the size of 
walnuts before use; otherwise, irregularities in running may be 
anticipated, especially in small furnaces. Minerals containing any 
considerable proportion of silicate of magnesia should be avoided. 

It seems hardly necessary to mention that the simple fusion 
of unroasted matte in a cupola furnace produces practically no re¬ 
sult except a change of form, the removal of sulphur by sublima¬ 
tion being so slight as to cause an enrichment of only one or two 
per cent. 

Although this subject has been already briefly discussed, there 
exists such a widespread idea among non-professional men that a 
mere fusion of the matte is sufficient to increase its value that a 
positive statement to the contrary, accompanied with some ex¬ 
periments which were executed to demonstrate this fact to a 
doubting director of a smelting company, may prove of value in 
some future instance. Twenty-six tons of carefullv sampled un- 
roasted matte, broken to the size of an egg, were smelted in ten 
hours in a cupola furnace with a wind pressure of one inch mer¬ 
cury. Ten per cent, of ordinary ore slag was added, to protect 
the metal. 

On accurately weighing and sampling the product of fusion, 
the following results were obtained: 


Weight of matte smelted.26*00 tons. 

Weight of slag smelted. 2'60 tons. 

Assay of matte smelted.33*50 per cent. 

Assay of slag smelted. 0*37 per cent. 

Weight of matte produced.25*07 tons. 

Assay of matte produced.34*70 per cent. 

Assay of slag produced. 0*32 per cent. 


Showing an enrichment of oidy 1*2 per cent. The amount of 
copper produced differs only 0*001 per cent, from the amount 
charged, showing a remarkable agreement in assays, weights, etc. 









GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


273 


Further experiments were made with corresponding results, 
although with more variation in the figures obtained. 

Notwithstanding the fusibility of the mixture, fully as much 
fuel is required in smelting roasted matte with its siliceous dux 
as in the case of calcined ore, one pound of good coke being re¬ 
quired for from 7 to 9 pounds of charge. This may result from 
the great quantity of reducing gases required to lower the sesqui- 
oxide of iron, which is usually largely present in roasted matte, 
to a protoxide, as well as to the greater tendency of metallic cop¬ 
per or very rich matte to chill in the bottom of the furnace, which 
must lie counteracted by an additional quantity of fuel. 

The same pattern of furnace used for smelting ore is also ap¬ 
plied to the concentrating fusion of matte, the height of Ameri¬ 
can copper cupolas seldom being so great as to unfit them for 
this work. 

The richness of the product depends on the thoroughness of 
the calcination, as well as on the extent of the reducing action in 
the smelting process. 

It is seldom that the calcination has been executed so thor¬ 
oughly as to yield solely metallic copper in fusion. A variable 
quantity of rich matte accompanies the metal. The grade of the 
copper may be also unduly reduced by metallic iron, as was the 
case in the Houghton slag smelting, where the anthracite used 
as fuel caused a large and unwelcome adulteration of the copper 
product with iron. 

This is, however, unusual in American practice, the lowness 

' ' i 

of the furnaces and the rapidity of the process combining to pro¬ 
duce a tolerably pure metal, as will be seen from the following 
partial analyses of pig-copper resulting from the fusion of roasted 
matte in the cupolas : 

Ely pig-copper (by Nolten): 

Iron. l’t> 

Sulphur. 0‘8 

Copper. 07‘2 

99-6 

Ely pig-copper (by Peters. Selling sample of 200,000 pounds): 

Iron. 

Sulphur. O'! 

Copper. 08 4 


100*2 










274 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Ore Knob pig-copper (by Griffith): 

Iron. 

Sulphur. 

Copper. 


A comparison of the foregoing determinations, which represent 
the average condition of very large quantities of black copper as 
produced in this country from the fusion of roasted matte, with 
the following analysis from Percy of the average black copper 
produced at Atvidaberg, Sweden, will show the advantages re¬ 
sulting from a more rapid execution of the process and other im¬ 


provements : 

Copper. 94‘39 

Iron. ^’04 

Zinc. 1'55 

Cobalt and nickel. d'63 

Tin. 0-07 

Lead and silver. 0’30 

Sulphur. 9’80 


99-78 

An average sample of pig-copper from the Detroit and Lake 
Superior Smelting Company’s cupolas at Houghton contained 
only 94 per cent, copper, the remainder being principally sulphur 
and iron. This extreme impurity, from such remarkably clean 
metallic ores, arises from the sulphur in the anthracite used as 
fuel, and the excessively powerful reducing action, especially 
when it is charged in the ratio of about one pound to each four 
pounds of material smelted. 

The presence of zinc, cobalt, nickel, etc., in Dr. Percy’s sam¬ 
ple of Swedish copper will account in part for the low grade of 
the black copper, but the principal reasons for the difference in 
quality are those already mentioned. 

Three samples of black copper from the celebrated Mansfeld 
works in Prussia, made respectively by Bertliier, Hoffman, and 
Ebbingliaus, contained 95*45, 89*13, and 92*83 per cent, of copper; 
while two determinations of the same material from the Riechel- 
dorf smelting-works, in Germany, by Genth, give respectively 
83*29 and 92*24 per cent, of metal. 

The influence exercised on the succeeding operations by the 
purity of this product is very great, the lower grades of black 


1-4 

1-1 

96-8 


99-3 














GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


275 


copper requiring one or more oxidizing fusions to bring them 
to the same purity as that already possessed by the immediate 
product of most American furnaces used for the production of 
pig-copper. 

The product of matte concentration in blast-furnaces differs 
from that derived from the same process when executed in rever- 
beratories in not being homogeneous, but consisting usually of a 
matte of medium high grade, together with a certain proportion 
of metallic copper, where, in the latter case, it would consist en¬ 
tirely of a matte of very high grade. This is a most interesting 
fact, and yet awaits a satisfactory explanation. 

The large brick furnaces already described are also used with 
advantage for matte concentration, their principal drawback be¬ 
ing the inevitable tying up of a large quantity of metal in the 
bottom of the cupola. This deposit increases according to the 
quantity smelted, and even in a well-constructed furnace may 
amount to 20 tons or more. This drawback will doubtless be 
eventually overcome, but for the present prohibits the employ¬ 
ment of such cupolas for the purpose indicated for any but very 
large metallurgical concerns, which can afford to submit to the 
locking up of such a large amount of metal for the sake of the 
economical advantages belonging to this type of furnace. 

TREATMENT OF FINE ORE IN BLAST-FURNACES. 

The mechanical condition of the ore to be smelted in blast-fur¬ 
naces is a matter of scarcely less importance than its chemical 
constitution. 

The evils resulting from, an undue proportion of fines are 
well known. 

The formation of an immense quantity of flue-dust is one of 
the least of these evils, as provision can be made for its collection 
and reworking, though at an increased cost; but the difficulties 
resulting from the choking of the furnace, and the sifting of the 
fine ore through the charge until it pours out in a stream through 
the tuyere-openings, scarcely altered by its passage through the 
furnace, are radical, and incompatible with either proper or 
economical work. 

The extent of this evil has encouraged the invention of a great 
variety of methods for its removal, most of them relating to a 
consolidation of the fine material into lumps of a suitable size. 


276 MODERN AMERICAN METHODS OF COPPER SMELTING. 

The agglomeration of the fine ore in the calcining-furnace has 
been suggested; but the great expense of fuel and the heavy 
losses inseparable from a method that, however applicable to such 
an easily fused substance as silicate of lead, would be entirely 
impracticable when dealing with oxide of iron, render it unneces¬ 
sary to discuss this practice. 

Assuming that the only feasible remedy consists in forming 
the fine ore into blocks, the experiments executed naturally fall 
into three divisions: 

1. Bricking by the aid of some foreign substance that has the 
power of holding the ore particles together. 

2. Bricking by pressure alone. 

3. A combination of the two methods. 

The materials tried by the writer and included under the first 
heading are: Silicate of soda (soluble glass), unslacked lime, 
clay, hydraulic cement, coal-tar and similar substances, sulphate 
of iron. 

In nearly all cases, a certain degree of pressure must lie used 
to form or mold the mixture into the desired shape; this may be 
obtained by an ordinary brick-machine, or by compressing with 
the hands, using a mold or not. In No. 2, pressing alone is used. 
A thorough mixture of the ore with silicate of soda results merely 
in the coating of each particle with a layer of soluble glass, and 
in nowise facilitates the agglutination of the ore. On the other 
hand, when the latter is already compressed into balls or blocks, 
the dipping of the same into a strong silicate of soda solution is 
accompanied with great advantage, the surface becoming, on dry¬ 
ing, nearly as hard as granite, and effectually preventing any 
wastage or breakage of the lumps by handling. (It should be 
mentioned that the circular or oval shape is much preferable to the 
rectangular, owing to the absence of fragile edges and corners.) 

Of course, this material would be far too expensive for any¬ 
thing but the richest ore, sufficient water-glass to thoroughly 
coat a ton of balls the size of the fist costing, at Eastern whole¬ 
sale prices, about $3.25. 

No substance has been more frequently employed for the pur¬ 
pose indicated than freshly burned lime, which should be slacked 
with considerable water, and the resulting milk of lime thoroughly 
incorporated with the ore, until the entire mass possesses the con¬ 
sistency of very thick mortar. 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


277 


This is usually left in a heap for several days, and then fed 
into the furnace in the shape of partially dried mud. But much 
better results are obtained by forming it at once into balls and 
subjecting it either to the hot sun or to a gentle artificial heat 
until it is thoroughly dry and hard. The resulting balls are 
somewhat brittle and fragile, and demand careful manipulation; 
but are far preferable to the product obtained by leaving it in a 
heap, and exert a marked effect in the capacity and condition of 
the smelting-furnace. 

The proportion of lime necessary to effect a good result varies 
greatly, according to the physical condition of the ore, the amount 
of sulphates present (which form a strongly cohesive cement with 
the lime), etc., but is usually from 5 to 12 per cent.—less than 5 
per cent, seldom producing satisfactory bricks. The cost of mix¬ 
ing alone (lime not included) is from 25 to 40 cents a ton by con¬ 
tract, which sum must be doubled or trebled if it is formed into 
bricks, depending upon the effectiveness and convenience of the 
plant. In almost all cases, the addition of lime has a favorable 
effect upon the subsequent fusion. It is probable that, when the 
water is removed from the lime by the heat of the furnace, the 
masses again crumble to a certain extent, but not until they have 
already undergone a certain preparation, which must be of value, 
to judge from the results obtained in actual work. This method 
was carried out extensively at the “ Gap n nickel mine, Pennsyl¬ 
vania, not only the roasted fines, but also the fine raw pyrites be¬ 
ing thus treated, previously to roasting in kilns; the results of 
the latter process being much better than could be expected from 
a material possessing such slight cohesive properties as fine gran¬ 
ular pyrites. 

The Orford Company and many other metallurgical establish¬ 
ments have adopted this method in the handling of finely pulver¬ 
ized, calcined matte, although in most cases the materials are 
simply mixed into a thick mortar, and charged into the furnace 
after lying in a heap for a few days. The difficulties and irregu¬ 
larities in the running of the cupola that would certainly result 
from the employment of an excessive proportion of such unfit 
material are counteracted to a considerable extent by the addition 
of a large amount of slag, which serves to loosen the charge and 
keep everything in normal condition. 

The important observation has also been made by Mr. W. E. 


278 MODERN AMERICAN METHODS OF COPPER SMELTING. 

C. Eustis, that a product of considerably higher grade results 
from the addition of some 5 per cent, of lime to the calcined 
matte. The substitution of limestone fails to produce the same 
effect. 

In consideration of the advantages already enumerated, and 
from the fact of its cheapness, general availability, and fluxing 
cpialities, lime may be regarded as the most useful substance yet 
known for the purpose under consideration, and where bricking un¬ 
der pressure, with subsequent thorough drying, is not attempted. 

Clay is also extensively used for the same purpose, and if 
thoroughly incorporated with the fine ore and allowed to dry for 
a reasonable time after being made into balls, gives a stronger 
and less friable product than lime. The quantity added varies 
from 2 to 5 per cent. 

It possesses the serious disadvantage of adding to the sili¬ 
ceous contents of the ore. In the case of calcined matte or highly 
basic ores, on the contrary, it forms a useful flux. The cheapest 
variety of clay that possesses the required plasticity should, of 
course, be selected. 

The powerful cohesive qualities of ordinary hydraulic cement 
long since attracted notice. 

Fortified by the favorable opinion of Prof. J. Fraser Torrance, 
the writer has employed it to brick jewelers’ sweeps, and after a 
month’s trial, is quite satisfied with the results obtained. 

He finds about eight per cent, of cement necessary to produce 
balls which, after a week’s exposure to the air, will bear moderate 
handling, and give good results in the furnace. Of course, the 
expense of this method forbids its use for ordinary substances. 

Where coking coal is available, fine ore can be mixed in large 
proportions with the coal in the kiln and coked. 

Coal-tar and similar substances require the aid of quite pow¬ 
erful compression to answer the required purposes, and have not 
been found practicable. 

A solution of copperas—sulphate of iron—is used in several 
of the European works to agglomerate fine ore. By careful dry¬ 
ing, the balls made with this substance become very hard; but the 
addition of sulphur to the charge (forming a perceptible increase 
of matte in cupola work), the very disagreeable effect upon the 
skin of the operatives, and other minor disadvantages, have pre¬ 
vented its adoption. 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


279 


The introduction of inexpensive machines for the manufact¬ 
ure of brick from almost dry clay, and capable of exerting an 
immense pressure, has opened new possibilities to the metallur¬ 
gist. Although, doubtless, such exist, the author can find no re¬ 
corded results of bricking fine ore by employing pressure alone, 
and is therefore obliged to fall back upon some brief trials made 
under his directions at the Parrot Works, Butte, Montana. The 
ore used consisted of pyrites concentrates, calcined so thoroughly 
as to contain only traces of soluble sulphates. The brick-ma¬ 
chine used produced about 40 bricks a minute, weighing 5 pounds 
each dry, and exerted a pressure of 4 tons per square inch. Un¬ 
der this immense force, the compressed ore slabs already pos¬ 
sessed considerable strength, and could be backed up in the usual 
manner. 

Unfortunately, no provision had been made for drying the 
brick by artificial heat—a most essential part of the process. 
After a day’s exposure to the air, they were smelted in a water- 
jacket furnace, breaking up to a considerable extent during trans¬ 
portation, but fusing with much greater rapidity and economy 
than when in a fine condition. 

A few that were dried at a gentle heat for six hours became 
so hard as to bear any reasonable handling, and when broken 
once in two, were admirably adapted for blast-furnace work. 
Rapid drying is highly injurious. 

The writer is quite convinced of the value of this method, and 
considers it applicable to any ordinary material. 

The essential conditions, after obtaining the proper pressure, 
are a gentle and sufficiently prolonged temperature, and a suffi¬ 
cient space to dry the necessary quantity. A series of light 
shelves in a well-ventilated building, heated by steam-pipes, would 
seem to fulfill these requirements, while the shape and size of the 
molds could be adapted to the purpose. A round or oval shape 
is best, thus escaping the wear on sharp corners and angles. 

The cost of bricking fine ore in this manner in Montana did 
not exceed 50 cents a ton; a single machine, requiring 10 horse¬ 
power and the labor of 8 men, having a capacity of 60 tons in ten 
hours. 

A combination of the two foregoing methods was effected by 
incorporating a certain proportion of lime or clay with the fine 
ore, before submitting it to the immense pressure mentioned. 


280 MODERN AMERICAN METHODS OF COPPER SMELTING. 


The addition of from 2 to 4 per cent, of either of these sub 
stances was accompanied with an increase in the strength and 
tenacity of the product, and was found especially useful where 


the process of drying could not be carried out. V ith proper fa¬ 
cilities for a slow but perfect desiccation, no such addition is 


necessary. 

«/ 

Mr. O. K. Krause, President of The Vermont Copper Co., 
has obtained excellent results by stirring green fines into the 
molten slag from his black copper furnaces. From 75 to 100 
per cent, of the weight of the slag can be thus stirred in, the 
cooled mass being broken up and resmelted. 

In place of clay, fine slimes from the concentration department 
or other sources may be substituted, and their metal contents 
beneficiated at the same time. This practice was adopted by 
Prof. J. A. Church, at Tombstone, Ariz. An ordinary brick-ma¬ 
chine was employed, the cohesive property of the slimes being de¬ 
pended on to bind the fine ore together. 

Fine grinding has been lately proposed: it forms a pulp, 
which becomes tenacious from the minuteness of its particles. 
This plan is widely practiced in England for the balling of the 
raw Spanish pyrites fines, preparatory to their roasting in kilns. 
The tenacity generated in this otherwise granular and uncolie- 
sive material by a mere grinding is very striking. 

Before concluding this subject, the question of smelting fines 
in their natural condition should be noticed. 

While the presence in a cupola smelting charge of even a 
moderate percentage of fine ore is accompanied with certain evils, 
such as formation of flue-dust, the choking of the furnace, irregu¬ 
larities in its running, descent of the fine ore unprepared, until 
it even pours out of the tuyeres, scarcely heated above the tem¬ 
perature of the air, etc., it is a condition that is almost invariably 
met with to a certain extent, as the mere transportation of ore 
from one building to another will result in the formation of a 
certain amount of fines. It becomes important, therefore, to de¬ 
termine at what point the proportion of fines becomes so great as 
to demand measures for its relief. 

This again varies greatly with the quality of the ore, slag, and 
metal, the power of the blast, size of furnace, capacity and effi¬ 
ciency of dust-chambers, etc. 

Here, as in most other instances, no experiments have been 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 281 


recorded to determine this important point, and practice varies 
with the prejudice or opinion of every individual. 

The following experiments were made on ore from the Moose 
mine, in Park County, Colorado, in 1871, and though relating to 
the treatment of silver ore, will serve the present purpose as well 
as though the product had been a copper matte. The furnace 
was small—24 by 3 feet—and smelting an exceedingly infusible 
charge, containing over 40 per cent, of sulphate of baryta and 
much silica. 

The fuel was spruce charcoal, and the blast very weak, caus¬ 
ing an extremely slow smelting; but as the conditions remained 
the same throughout all the experiments, the results possess some 
value. 

The material smelted consisted of ores from the Moose and 
adjoining mines, from which all that would pass through a 3-mesh 
screen had been separated, to be submitted to a calcination, the 
fine ore containing a much greater proportion of sulphides than 
the coarse, which latter was smelted raw. 

To this coarse ore was added a certain amount of carbonate 
of lead ores, almost free from fines and the requisite quantity of 
heap-roasted auriferous iron pyrites, to produce a fusible slag. 
The latter material contained, after roasting, about 25 per cent, 
of fines; and the mixture as prepared for the furnace, and with¬ 
out the addition of the fine calcined silver ore, carried about 12 
per cent, of fines that would pass a 6-mesli screen. 

This was regarded as the normal charge, to which, by way of 
experiment, were added varying proportions of the roasted fines; 
all other conditions remaining as nearly identical as was practi¬ 
cable throughout the trials. 

Representing the quantity of this normal charge that would 
be smelted in twenty-four hours by 100, the addition of fines pro¬ 
duced the following decrease: 


10 per cent, fines reduced it to 


20 

it 

it 

it 

25 

tt 

tt 

tt 

30 

tt 

It 

it 

35 

(i 

tt 

it 

40 

It 

a 

tt 

50 

It 

it 

tt 


92 

80£ 

80 

64 

56 

51 

42 


Aside from the decrease in capacity accompanying the addition 









282 MODERN AMERICAN METHODS OF COPPER SMELTING. 

of fines, serious irregularities in tlie running of the furnace were 
also produced, causing an increase in the cost of smelting per ton, 
as well as greatly adding to the labor of the men and to the pro¬ 
portion of silver lost in the slag. 

An increase in the area of the furnace greatly heightens its 
capacity for smelting fine ore; and the results obtained in this 
direction by the use of the large Orford furnace are very striking. 

The presence of from 15 to 20 per cent, fines seems to be no 
drawback at all, when this type of furnace is employed, and even 
from 50 to 00 per cent, of the charge may consist of this ordi¬ 
narily unwelcome substance without seriously affecting the run¬ 
ning of the furnace, although, of course, its cajmcity will be some¬ 
what reduced. 

After smelting a charge containing a very high proportion of 
fines for from 24 to 36 hours, it will usually be found that cold, 
unaltered fines appear at the tuyeres. This results from the con¬ 
stant agitation of the charge by the blast, by which the ore par¬ 
ticles are sifted down through the interstices between the fuel 
and coarse ore, until they actually reach the level of the hearth. 
In such cases, the pipes should be removed and all the fine ore 
within reach raked out of the tuyere-holes, with appropriate 
tools. 

All feeding from above should now cease until the charge, 
under a light blast, has sunk nearly to the tuyere level, when the 
shaft should be refilled with alternate layers of fuel and coarse 
ore in the usual proportions, after which the use of fine ore may 
be resumed. With these precautions, a very large proportion of 
fine ore may be smelted in this type of furnace, without seriously 
diminishing its capacity or producing any irregularities of im¬ 
portance. 

The attention of metallurgists is particularly called to the ease 
with which raw fine pyrites, technically called “ green fines,” may 
be treated in this furnace with the fan-blast. This material often 
accumulates in great quantities at copper mines, as, owing to its 
mechanical condition, it cannot be roasted in heaps, while pecuni¬ 
ary considerations may forbid the erection of an extensive calcin¬ 
ing plant for its treatment. Heretofore, when of low grade (from 
1£ to 3J per cent.), it has been either thrown aside in heaps, or 
allowed to harden and consolidate until it can be broken out in 
lumps and added to the roast-heaps. By this practice much waste 


GENERAL REMARKS ON BLAST-FURNACE SMELTING. 283 


occurs, while a large amount of money is constantly tied up in 
this material. 

After experimenting, Mr. J. L. Thomson, of the Orford Com¬ 
pany, found that a charge composed of this material and ferrugi¬ 
nous slag from the concentration-fusion of copper matte could he 
smelted together to great advantage in the large furnace; the im¬ 
mense volume of blast employed oxidizing the raw pyrites to a 
considerable extent, and producing a matte of much higher grade 
than would result from such material under ordinary circum¬ 
stances. The slag from matte concentration always carries nearly 
or quite enough copper (from 1 to 2 per cent.) to cover the cost 
of its resmelting where fuel is cheap ; while the large percentage 
of protoxide of iron that it carries neutralizes the silica of the 
green fines, which finds no base in its own composition, all the 
iron that it contains being combined with sulphur, and conse¬ 
quently unavailable for slag formation. 

Where circumstances do not favor the employment of the 
matte slag, this may be replaced by heap-roasted pyritic ore; 
in which case, of course, the resulting matte will be somewhat 
richer. 

In any case, the slag resulting from, this practice is distin¬ 
guished by its freedom from copper, owing to the overwhelming 
amount of low-grade matte present, which cleanses the fight sili¬ 
ceous slag to an unprecedented degree. Owing to the large 
amount of unsatisfied silica in the green ore, the slag is always 
exceedingly acid, containing from 48 to 55 per cent. Si0 2 , and 
often being so sticky and thick that only the constant and power¬ 
ful stream of intensely hot, low-grade matte keeps the slag-run 
open, and prevents the furnace from “ sticking up.’ 7 

The oxidation of the fine sulphide particles by the air-blast 
carries the heat to the surface of the charge, and produces to a 
certain extent those evils inseparable from the extension of the 
high temperature from the zone of fusion to the upper layers of 
the charge. Owing to these circumstances, a serious burning of 
the brick walls often takes place, which circumstance, combined 
with the cutting down of the furnace bottom from the immense 
quantity of fiery, low-grade metal, favors the practice already 
recommended of keeping in blast only during twelve hours out 
of the twenty-four. 

The siphon-tap is almost indispensable in this form of smelt- 


284 MODERN AMERICAN METHODS OF COPPER SMELTING. 

ing, as the quantity of matte produced in a twenty-four hours’ 
run often amounts to 25 or 80 tons. 

From six to nine months has been the ordinary length of 
campaign for these large brick furnaces, running on either a sili¬ 
ceous or basic slag, at the expiration of which time a week’s re¬ 
pairs will again tit them for work. 

Not feeling at liberty to give the results obtained in the fusion 
of green fines at the Orford Works, where this practice originated, 
the author is forced to fall back upon results in his own practice, 
where the total quantities treated, though much smaller, still ag¬ 
gregate some 30,000 tons. During a four months’ campaign, in 
which a mixture of green fines and matte slag were treated in a 
large Orford furnace, the average daily (twenty-four hours) re¬ 


sults were as follows: 

Weight of green fines smelted. 49*71 tons. 

“ “ matte slag “ 38*40 “ 

Total. 88*11 

Gas-coke used. 16*10 tons. 

Assay of ore. 3*87 per cent. 

Assay of matte slag. 0*94 u 

Weight of matte produced. 20*67 tons. 

Assay of matte produced. 10*70 per cent. 

Assay of slag produced. 0*13 “ 


Rate of concentration, about 2^ tons of ore into one. The 
copper produced in this campaign, after taking into considera¬ 
tion the metal gained in the matte slag, and deducting the small 
amount lost in the slag from the operation itself, agreed almost 
exactly with the amount calculated from the careful and frequent 
assays made. 

The matte produced, though very low in grade, is roasted in 
heaps with great facility, and forms a most welcome flux for sili¬ 
ceous ores. 

This practice is unique and well worthy of attention. 

The size to which ore must be broken for cupola smelting de¬ 
pends upon two factors—its fusibility and its conductivity. 

Fusible material, especially if porous—such as ferruginous 
and calcareous ores, basic slag, etc.—may be charged in frag¬ 
ments from 3 to 5 inches in diameter without producing evil re¬ 
sults, although good practice demands its pretty uniform reduc¬ 
tion to the size of a large apple (that is, fully 3"). The same may 












GENERAL REMARKS ON BLAST-FURNACE SMELTING. 


285 


be said of fragments of copper matte or metallic substances, 
which, being* excellent conductors of heat, melt all at once, where 
a piece of quartz or fire-clay might be in a state of fusion on the 
surface, while hardly heated at the center, and consequently 
should be invariably reduced to the size of horse-chestnuts, un¬ 
less smelted in company with a large proportion of basic ore. A 
striking example of this may be found in the fusion of u mass 
copper ” at Lake Superior, where pieces of this metal weighing 
five or six tons are smelted on the hearth of a reverberatory fur¬ 
nace with no difficulty or delay, the high conductive power of 
copper causing an equal distribution of heat and simultaneous 
fusion of the entire mass. A rock of the same size could never 
be smelted except by the gradual wearing away of its exterior 
surface. 

The following resume is from a paper on Copper Smelting by 
H. M. Howe, in the Bulletin of the United States Geological Sur¬ 
vey. 

RESUME. 

To sum up, for smelting ore the cupola is especially advan¬ 
tageous— 

I. With highly ferruginous ores. 

II. Where the cost of anthracite, coke, or charcoal is not ex¬ 
cessively greater than that of bituminous coal, wood, and other 
fuels fitted for the reverberatory only. 

III. For oxidized ores. 

IV. For low-grade native copper. 

V. Where, as in the case of lean ores, clean slags are a neces¬ 
sity. 

The reverberatory is especially advantageous— 

VI. With highly refractory siliceous, aluminous, calcareous, 
or magnesian ores. 

VII. Where the composition of the ore changes suddenly and 
greatly. 

VIII. Where bituminous coal, wood, or other reverberatory 
fuel is very much cheaper than anthracite, coke, or charcoal. 

IX. For smelting and immediately refining rich native cop¬ 
per. 

X. Its disadvantage in yielding richer slags than the cupola 
weighs less heavily in case of rich ores. 


CHAPTER XII. 


LATE IMPROVEMENTS IN BLAST-FURNACES. 

The principal changes have been in the general arrangement 
of the smelting plant, in improving certain details, and in effect¬ 
ing some slight economies. 

Herreshoff has designed in connection with his furnace an ex¬ 
cellent charging platform, consisting of flanged cast-iron plates 
bolted together, surrounded by a rail of ordinary one-inch gas 
pipe and supported by girders in such a manner that there are 
no posts to interfere with the work about the furnace. 

Finding that the cast-iron plates forming the floor of the fur- 
nace-slied soon become warped and destroyed by the stream of 
hot slag falling upon them every time that the slag-pots are 
changed, I have remedied this difficulty by cutting a circular hole 
sixteen inches in diameter in the plate, directly where the slag 
stream falls, flanging the same, and providing it with a cast-iron 
basin, which is kept filled with sand and can be changed at will • 
the wheels of the slag-pot straddle this basin so that it does not 
interfere at all with the work. 

When running on a low-grade copper matte, and more espe¬ 
cially if producing a matte containing nickel, the bronze tapping 
ring used in connection with the Herreshoff fore-hearth soon be¬ 
comes porous and leaky, so that if not changed at once, the liquid 
matte is certain to eventually get into the water space and pro¬ 
duce a dangerous explosion. No amount of care in casting this 
bronze alloy seems to help matters. The addition of a small 
percentage of silicon was tried, but neither did this, nor the 
addition of aluminum, help matters. 

Molten tin and solder were poured into the bronze casting, 
and it was then shaken until the interior was plated with a thick 
layer of this malleable metal, but without avail. The minute 
holes that appeared in the tapping ring could neither be plugged 
nor corked, as the metal became brittle and rotten, and crumbled 
under the slightest blow. 


LATE IMPROVEMENTS IN BLAST-FURNACES. 


At one time, when running some one hundred and thirty tons 
of ore a day, and producing twenty tons or more of matte con¬ 
taining some 18 per cent, nickel and 20 per cent, or more of cop¬ 
per, it became necessary to change the tapping rings every three 
or four days, owing to the trouble just mentioned. 

After much experimenting it was found that, by reducing the 
quantity of feed water to a minimum, and thus keeping the tap¬ 
ping ring constantly at a temperatime of nearly 200° Fahrenheit, 
the trouble was remedied to a great extent ; and this method has 
been pursued ever since. 

Of course, whenever a pot full of matte is tapped off, it is 
necessary to let on a little more feed water for the moment. 

Another very important precaution to take, especially when 
running furnaces with a narrow water space, where the feed 
water is not absolutely pure and free from every trace of sedi¬ 
ment, is to provide the furnace with additional discharge pipes 
at all points where the heat is great and the circulation of the 
feed water is liable to be sluggish or impeded by sediment or lime 
salts; such places are the very narrow space between the main 
outlet hole of the furnace and the iron ring that forms the lower 
border of the jacket, and also that between the main tap-hole 
casting in the furnace proper and the same lower border. 

A half-inch pipe screwed into a hole tapped through the lower 
ring and discharging into the same funnel as the waste pipes from 
the fore-hearth and tap-hole casting, and provided with a valve 
to regulate the flow of water, may prolong the life of a water 
jacket for many months. 

The cast-iron fore-hearth or well used in connection with the 
Herreshoff furnace is, according to my experience, very liable to 
crack long before it is worn out. This is especially the case in 
cold weather, when a furnace is frequently cooled down and 
started up again. Such cracks can usually be temporarily re¬ 
paired by covering them with red lead, or with a mixture of sal- 
ammoniac and iron filings over which a plate of wrought-iron is 
to be accurately fitted and tightly screwed down. But I have 
found that in the end a weli made entirely of wrought-iron is 
more economical and satisfactory. I have had a separate water- 
jacketed slag-spout made for these wrought-iron wells , as it makes 
their construction so much simpler. 

As the matte when tapped often streams into the pot with 


288 MODERN AMERICAN METHODS OF COPPER SMELTING. 

such force as to cause waste, it has been found advantageous to 
diminish the pressure in the fore-hearth by letting the blast es¬ 
cape into the air during the actual operation of tapping. This 
is most easily accomplished by cutting a large opening in the 
blast pipe close to the furnace and providing it with a hinged 
door that is kept tightly closed by a weight, except during the 
moment of tapping, when it is opened by pulling a w T ire. 

When 100 to 150 tons of slag are run out of a copper furnace 
in a single day, it becomes not only difficult to handle it in pots, 
but the wear and tear of the pots amount to a very heavy item. 
The small scale on which copper works are usually built, prevents 
the adoption of the methods used at handling slag at the great 
iron furnaces, where it is usually flushed pff in great quantities 
and at considerable intervals of time, instead of running in a 
continuous small stream. Where water is obtainable, no better 
method can be adopted than to granulate and remove the slag by 
means of a stream of water. A considerable pressure is required, 
and the secret of using this method with success is to strike the 
falling stream of slag with such a forcible stream of water as to 
granulate it instantaneously and sweep it off over the dump. A 
stream of water three inches in diameter under a head of ten feet 
should easily handle the slag from a 150-ton furnace, and would 
require a fall of nearly an inch to the foot. 

Where the roasting has been imperfect and it is more a ques¬ 
tion of obtaining a tolerably rich matte than of putting a large 
quantity of ore through the furnace, it is possible to drive off 
much of the remaining sulphur by running with only two or 
three feet of charge above the tuyeres and using a very light 
blast. This naturally means a high consumption of fuel, but 
will produce a very rich matte. It is by this method that the 
German black copper furnaces and the small copper furnaces at 
Ely, Yt., produce a large proportion of very pure black copper 
from an imperfectly roasted, 80% matte. That it is the slow 
smelting that accomplishes this removal of the sulphur is well 
shown by the following amusing, but very instructive incident: 

At a certain smelting works where the copper furnaces just 
at that time were running on a very low-grade matte, that was 
also very badly roasted, the manager suddenly received a visit 
from several directors of the company. Naturally wishing to 
make a good showing at the furnaces, he sent out the order to 


LATE IMPROVEMENTS IN BLAST-FURNACES. 


289 


throw half a dozen pigs of black copper into each of the cupolas 
and put on a heavy blast. In the course of half an hour, deem¬ 
ing that the dose would have its effect, he arrived opposite the 
copper furnaces with his visitors, and ordering them to lie tapped, 

conlidentlv awaited the metallic flood that was to astonish the 
«/ 

directors and lubricate the finances of the company. But instead 
of copper, the only result obtained was an immense tap of matte 
of medium grade. The manager’s chemistry was so deficient that 
he had failed to realize the fact that little or no sulphur would be 
volatilized during such rapid smelting, so that it was bound to 
combine with such metallic copper as it could find in the fur¬ 
nace, thus not only producing no copper from the original 
charge, but actually u throwing back ” into matte all his extra ad¬ 
dition of metallic copper; so that whereas slow running on a poor 
charge will produce a large proportion of pig copper, rapid run¬ 
ning on a rich charge may produce nothing but a matte of toler¬ 
able grade. 


CHAPTER XIII. 


THE SMELTING OF PYRITOUS ORES CONTAINING COPPER AND 

NICKEL. 

The occurrence of a nickeliferous pyrrliotite containing a 
more or less plentiful admixture of clialcopyrite seems peculiar to 
the Huronian and Laurentian systems, and lias been so exten¬ 
sively discovered in Northern Ontario, and so largely worked 
both for the copper and nickel it contains, that, in view of the 
interest that is at present shown in these mines, and the intimate 
connection that their treatment has with the general metallurgy 
of copper, it seems proper to introduce a short description of the 
most approved methods now employed for treating these ores. 

As it fell to the lot of the author to assist in opening the first 
mines and build the first smelting works in the district referred 
to, and manage them for a couple of years, he is enabled to de¬ 
scribe these matters without deviating from the policy pursued 
throughout this work of speaking authoritatively of only such mat¬ 
ters as have come under his personal observation and within the 
sphere of his own practice. 

The geology and mode of occurrence of these ores have no 
bearing upon their treatment. Suffice it to say that the nickel¬ 
iferous pyrrkotite occurs mainly in lens-shaped bodies situated in 
diorite dikes that cut through the country rock for a long dis¬ 
tance, but that only carry bodies sufficiently concentrated to be 
of commercial value at certain points where the local conditions 
have been favorable for its deposition. 

The pyrrliotite occurs in a very massive form usually, and 
seems to have a portion of its iron replaced by nickel without the 
proportion in which the latter metal occurs affecting the physical 
structure or appearance of the pyrrliotite. The amount of nickel 
in the pure pyrrliotite varies from 14 to 9 per cent., averaging 
perhaps 4 per cent. But the admixture of diorite, clialcopyrite, 
and other foreign matter reduces the ores treated on a large scale 
to perhaps per cent, of nickel. There are exceptional ores 


THE SMELTING OF PYRITOUS ORES, ETC. 


291 


that carry 15, even 20 per cent, of nickel, and some few crystals 
of pure Millerite (sulphide of nickel) have been found in depth, 
but these rare exceptions have no effect on the general average. • 

The copper content of the ore is a foreign admixture, and oc¬ 
curs solely in the shape of a very pure chalcopyrite, carrying very 
nearly its proper theoretical proportion of copper (about 31 per 
cent, when pure). This is at times scattered throughout the 
pyrrliotite in specks and thread-like veins; at other times it oc¬ 
curs in nodules of considerable size, while rarely it is found in 
almost massive condition, between the vein of pyrrliotite and the 
wall-rock. 

On an average, the ore treated at the principal mines carries 
some 1 per cent, of copper, though if selected, it could easily be 
brought up to 8 or 10 per cent. But up to the present time, ex¬ 
perience has shown that it pays about as well to mix all the ores 
and smelt them as they are, as to try to make two grades of 
matte, one rich in copper and poor in nickel, and the other high 
in nickel and low in copper. By pursuing the latter course, a 
slightly better price can Vie obtained from the refiners, but the 
metallurgical operations are seriously embarrassed, as, if the 
heavy nickel ore is smelted alone, it produces far too basic a slag; 
while if the richer copper ore is fused by itself, the slag is too 
siliceous to smelt easily. By mixing the two varieties of ore in 
their proper proportions, a good slag is obtained without the ad¬ 
dition of flux, not a pound of the latter being used during the 
time I was in charge of the work. Besides, the ores roast much 
better when mixed than if separate. 

ROASTING. 

The ore, after being run through jaw-breakers at the mines, 
set to about 1J inches, is run in railroad cars to a high trestle, 
which extends the entire length of the roast-yard, and from which 
the ore is dumped directly upon the heaps. 

These are made very large, about 40 by 80 feet, and some 6 
feet high. Sound pine wood is used for the bed. and about one 
cord of wood is laid down for each 20 tons of ore in the heap. 
It is laid with great care, leaving air-channels to the center of the 
pile, while the surface of the wood is evened off with chips and 
smaller wood, and everything possible is done to obtain strict 
uniformity of combustion. After the main body of the heap is 


292 MODERN AMERICAN METHODS OF COPPER SMELTING. 

formed of the coarse ore, the ragging, or middling-sized ore, is 
added, being about a foot thick at the base of the pile, and taper¬ 
ing up to a few inches at the top. The fines are lastly added in 
the same way, though not so thickly at first, and a considerable 
additional supply of the latter is placed in heaps around the pile, 
in order to smother the fire after it is started. 

The heap is fired at night, on account of the smoke, and when 
possible, it was found best to wait until several piles were ready 
and then fire them all at once, thus concentrating into one short 
period the harassing escape of fumes that would otherwise annoy 
the workmen who were building up or tearing down neighboring 
piles, just as much every time each single one was lighted. 

A skilled and trusty man attends to the kindling and watch¬ 
ing of the heap, and usually has to spend the entire night in 
working at it; filling up holes that appear from the burning away 
of the wood, and consequent sinking of the superincumbent ore; 
adding fines to those portions of the surface which appear too 
hot, and giving vent to those parts that show no sign of life. 
The entire success of the roast depends upon the building and 
fighting of the heap and its management during the first few 
days, and especially the first 24 hours. 

And at this point, it may not be amiss to again call attention 
to the vital importance of having a proper and well-drained roast- 
ground. In the severe climate of Northern Ontario, it was some¬ 
times necessary, in inaugurating a new plant, to build a heap on 
frozen ground, or ground that was not thoroughly drained. In 
both cases the results were miserable, the escaping steam seeming 
to completely impede the combustion, and the resulting heap, 
when torn down, revealing isolated spots, each containing many 
tons of ore that were not roasted at all, only the surface being 
slightly scorched, though the greatest pains were taken in build¬ 
ing and managing the heap. 

An absolutely dry and unfrozen ground is essential to suc¬ 
cess, and if snow falls, it must be carefully cleared away before 
laying the wood down, and after the wood is once in place, no 
snow or rain must fall upon either the fuel or ore. This can be 
protected by coarse canvas or boards, and well repays the labor 
and expense. I am not speaking of the slight rains and snows 
of more genial climates, but of the heavy Arctic storms of this 
northern country. 


THE SMELTING OF PYRITOUS ORES, ETC. 


293 


Where the ground is frozen, the results of the roasting are 
always extremely unsatisfactory. A few hours after lighting the 
heap, water begins to flow out from under it, and for a day or 
two, a continuous stream will pour out from the lower side of 
the pile, generating steam in quantities, and extinguishing the 
fire as soon as the lumps of ore are scorched a little on the out¬ 
side. 

The size to which the ore must be crushed is another most 
important factor in heap-roasting. Some ores, especially the 
ordinary iron pyrites or bisulphide of iron, can be dumped on 
the wood in lumps as large as a child’s head without seriously 
affecting the results. Under the influence of the intense heat, 
these lumps crack asunder, and the fire penetrates into every 
crack and fissure, and eventually oxidizes every atom of the 
bisulphide. But with most monosulphide or pyrrhotite ores, the 
case is different, and the nickeliferous Sudbury pyrrhotite is per¬ 
haps the hardest of all ores to roast. Not the slightest swelling 
or fissuring of the lumps occurs, and the oxidation seems to pene¬ 
trate only a certain short distance from the surface of the piece 
of ore. If the diameter of the lump is more than twice as great 
as the average depth of this penetrating zone of oxidation, there 
will always be found a central kernel entirely unchanged and 
unaffected by the roast. 

It is essential, therefore, to set the crushers very close, If to 
If inches between jaws, and to keep them so, as the wear of the 
jaws will rapidly increase the size of the opening if they are not 
constantly attended to. 

Owing to this necessity, a greater amount of the ore is 
crushed into ragging and fines than can be used to cover the 
heap in the ordinary manner. It is better to treat the surplus 
by itself than to run the risk of damaging the entire roast by 
covering the heap too closely. 

The ragging may be roasted advantageously in a heap by 
itself, by dumping first a layer of coarse ore upon the wood, and 
then completing the heap with ragging, which should not, how¬ 
ever, be much over two feet thick at any point. This low heap 
is covered lightly with fines, and will burn out in a couple of 
weeks. Very good results may thus be obtained. 

But a greater difficulty is presented in dealing with the sur¬ 
plus of fines. I know of no better plan than to lay them down 


294 MODERN AMERICAN METHODS OF COPPER SMELTING. 

some G to 10 inches thick upon the ground where a fresh heap is 
to he built. The wood is then placed upon the fines, and the 
heap constructed as usual. After one or two heaps are burnt on 
this foundation, it will be found that the fines have become oxi¬ 
dized for perhaps half their depth from the surface. This top 
layer is then removed with the ore, and the fresh heap built upon 
the bottom layer until it, in its turn, is ready to remove, when a 
fresh lot of fines may be laid down and the operation recom¬ 
menced. If all these points that have been described are care¬ 
fully attended to, there will be no danger of too low a matte from 
the first smelting. At Sudbury, we nearly always add unroasted 
fine ore (“Green Fines”) to the charge to prevent the formation 
of too rich a matte, with its accompanying evils. 

But ordinarily the roasting is carelessly executed, and the 
smelting suffers accordingly. The most important factor in suc¬ 
cessful roasting is to always have sufficient ore on hand and being 
mined, so that none of the operations at the roast-yard have to 
be hurried. If, at any works, it is found that the furnaces are 
living from hand to mouth, that roast-heaps have to be broken 
into while still hot and burning, and that there is always a hurry 
for roasted material, it is time to stop all smelting operations 
and secure an abundant supply of roasted ore. 

Nickel matte has many peculiarities of its own, and makes so 
many difficulties in handling, and in its property of welding to, 
and destroying, any iron surface that it touches, that it made us 
endless trouble at first till we learned how to handle it, no one 
before myself ever having tried to smelt nickel ores in such a 
furnace on a large scale. 

About 7 tons of ore should need one ton of Connellsville, or 
equally good coke. Pine charcoal at 6 cents per bushel would 
probably be just about as cheap as coke at $8.00 per ton, but in 
the northern climate, where it would certainly get wet and dam¬ 
aged, which does not harm coke so much, the coke w r ould be in¬ 
finitely more advantageous. Hard-wood charcoal at the above 
price might possibly be cheaper than coke. It would be so near 
equal that only experiment on a large scale would determine 
the matter, but in any case, it would probably pay to use J to J 
coke, as the furnace is under much better control with the denser 
fuel. 


THE SMELTING OF PYRITOUS ORES, ETC. 295 

TREATMENT OF THE NICKEL MATTE. 

In nickel smelting, when the matte is obtained, it still remains 
to be refined, and only those who have been through such an ex¬ 
perience realize the difficulties of disposing of it. 

In the first place, it becomes a question of calculation whether 
it will pay better to ship the matte at about a grade of 25 per cent, 
as it is produced from the furnace, or to concentrate it on the 
spot by a second series of roasting and smelting operations. 
Until the local conditions, wages, scale on which operations are 
conducted, exact character of ore that is treated, etc., are known, 
this question cannot be answered. The matte is enriched by 
roasting it and resmelting it in a water-jacket or other furnace 
with quartzose flux to take up the iron. It is a question to be 
determined by circumstances whether the roasting should be 
executed in heaps, as with the ore, or whether it should be 
crushed and calcined in a few hours in calcining furnaces. 
Heap-roasting of matte takes about as long as the ore, because it 
has to be re-roasted 2 or 3 times, as it does not roast freely like 
the ore. But as there is only about one-sixth so much to handle 
as of the raw ore, the expense per ton of ore is not heavy. A 
matte of about 50 to 60 per cent, of nickel is produced by the 
so-called concentration smelting. 

This concentrated nickel matte has a high point of fusion, 
and easily forms crusts and accretions. 

It is impossible to smelt it in a furnace with brick fore-hearth, 
as may be advantageously done with the *ore, for it soon fills 
up the front crucible, necessitating its substitution, and leav¬ 
ing a “ salamander,” weighing a ton or two, that is difficult to 
break up. 

After much experimenting, I have returned to the old prac¬ 
tice of using u steep,” or a mixture of pulverized coke and clay 
for a fore-hearth, cutting in it a small crucible connected with 
the furnace-crucible by a deep groove. Out of this crucible, the 
rich nickel matte can be either tapped or ladled into molds, and 
as this method of procedure involves frequent, though very 
slight, repairs, it will save much delay to make the fore-hearth 
broad enough to permit of two such crucibles, side by side. Thus 
one can be repaired and dried while the other is in use. 

The further treatment of the nickel matte, according to the 


296 MODERN AMERICAN METHODS OF COPPER SMELTING. 

old practice, is well known, and its description would be out of 
place in this connection. 

Being- expensive and slow, efforts are being made to improve 
upon it, and one of the principal nickel smelting companies at 
Sndburv is erecting a plant to Bessemerize this rich sulphide of 
copper and nickel. 

According to the laws of chemical affinity, as modified by the 
high temperature employed, we know that the iron still remain¬ 
ing in the matte ought to oxidize first, forming, with silica, a slag 
that may be poured off. Next the nickel should oxidize and 
slag away, leaving behind the pure copper. 

But whether such accurate results will be reached in practice 
seems to me somewhat doubtful. 

In the Bessemerizing process, as applied to iron, the entire 
mass of metal remains homogeneous throughout the operation, 
the impurities being gradually oxidized, until it is all converted 
into steel. And the total amount of these impurities is only 4 or 
5 per cent., so that the mass of fluid metal operated upon is not 
perceptibly lessened. 

But in Bessemerizing a mixture of the sulphides of iron, cop¬ 
per, and nickel, the number of different chemical compounds, 
having differing specific gravities and tending each to form 
its separate stratum in the converter, is too great to even enu¬ 
merate. 

As soon as sufficient sulphur is removed to correspond to the 
iron present, we shall have a layer of oxide of iron (combined 
with silica from the converter lining) on top, while below, the sid- 
pliides of nickel and copper will remain comparatively unaltered. 
Then may come a period, when we have the same silicate of iron 
on top, followed by a little silicate or oxide of nickel, whilst some 
metallic nickel has formed and sunk to the bottom, and the rest 
of the nickel, in its original condition of sulphide, forms a 
stratum below the unaltered sulphide of copper. 

These reactions and products increase in number and com¬ 
plexity as the operation advances, and remembering the great 
difficulties encountered in Bessemerizing even so simple a sub¬ 
stance as copper matte, one cannot help feeling some curiosity as 
to the practical success of this operation. 

That nickel and copper can be rapidly reduced from the con¬ 
dition of a matte to that of separated metals, the author has con- 


THE SMELTING OF PYRITOUS ORES, ETC. 


297 


vinced himself. But business considerations prevent the further 
elucidation of this subject. 

The final treatment of the nickel-copper alloy, or of the al¬ 
ready separated metals, does not fall within the scope of this 
work. 

But it must be evident to every one familiar with the facts, 
that the commercial electrolysis of copper on the one hand, and 
the electrolytic deposition of nickel in our nickel-plating estab¬ 
lishments, on the other hand, point out a path to follow that is 
too plain to be neglected. 

And as our chemists find no difficulty in precipitating, with 
the electric current, chemically pure copper from a solution con¬ 
taining both copper and nickel, and then, by slightly altering the 
conditions, precipitating all the nickel in absolute purity, from 
the same solution, and with the same current, it would seem that 
our refiners might reasonably expect to effect the same results on 
a commercial scale, especially as there is practically no loss of 
acid in the operation. 

Nor can I see any reason why nearly all our metallic nickel 
should be offered to the trade in little cubes less than an inch 
square. Of course, this peculiar form has resulted from the prac¬ 
tice of the nickel refiners to reduce the oxide of nickel obtained 
by the methods now in use to metallic nickel. Being mixed 
with rye meal, as a reducing agent, it is formed into these little 
cubes and a number of these packed in crucibles are exposed 
to a sufficient heat to reduce the nickel to a metal without 
fusing it. 

This makes a small, porous fragment of metal, suitable for 
solution in acids, and where nickel is to be used in minute quan¬ 
tities. 

But it adds materially to the expense of refining, and there is 
really no more reason why nickel should be so treated than cop¬ 
per or iron. 

Although the fusion point of nickel is rather high, yet a suffi¬ 
cient temperature to make nickel pour as readily as copper is ob¬ 
tained without difficulty in metallurgical practice, and there is 
little doubt that before long nickel will be refined in bulk and 
cast into suitable ingots, as is copper or lead. 

Indeed, at Vivian & Company’s nickel works in England, a 
small reverberatory, heated by gas, has been in use for several 


298 MODERN AMERICAN METHODS OF COPPER SMELTING. 

years for refining nickel, some 2,000 pounds being refined at 
a charge; and the superb display of solid nickel articles and 
ingots, made by Joseph Wharton of Philadelphia, shows that 
he experiences no difficulty in melting and casting nickel like 
other metals. 


CHAPTER XIV. 


REVERBERATORY FURNACES. 

This method of smelting copper ores is peculiarly English, 
the reverberatory furnace having practically had its origin in 
Swansea, where it has, during the past two centuries, undergone 
various changes and improvements, by which its capacity and 
economy have been considerably increased without any radical 
alteration in its original form or practice. 

The American reverberatories are modeled closelv after their 
English prototypes, and present no new features worthy of note, 
a constant tendency toward increased size and capacity being 
almost the only point in which any difference can be detected. 

This particular branch of metallurgy having engaged the 
attention of English and American authors to a greater extent 
than any other, nothing would be gained by a mere repetition of 
what may be found in the modern text-books, and the writer 
prefers to devote his own work to those practical details of con¬ 
struction and management that are yet wanting, and which he 
hopes may supplement the more strictly scientific information 
just referred to. 

While the blast-furnace has replaced the reverberatory to a 
considerable extent in the United States for ore-smelting, the 
latter is still generally preferred for matte concentration, and 
especially in its last stage, or the production of u blister copper.” 

The processes executed in the reverberatory furnace in this 
country may lie divided into the following classes, each of which 
demands separate consideration: 

1. Ore smelting. 

2. Matte concentration. 

a. By fusion of calcined matte. 

1). By an oxidizing smelting. 

3. Production of blister copper. 

4. Copper refining. 


300 MODERN AMERICAN METHODS OF COPPER SMELTING. 

As the first three of these processes are carried out in exactly 
the same type of furnace, their more detailed description may 
well he preceded by some consideration of the construction of a 
reverberatory furnace. 

The excavation for the foundations should be 18 inches in 
every direction larger than the proposed furnace, allowance being 
made for the space occupied by the stack or down-take at one of 
the front corners. A depth of 4 feet from the floor level is suffi¬ 
cient, and a permanent drain should keep the pit free of water. 
Exceptional circumstances may require a greater depth of so 
much of the excavation as corresponds to the foundation of the 
stack. Two longitudinal walls are now laid in such a manner 
that a 4-foot space is left under the main body of the furnace, 
extending from the 1 back of the ash-pit to a point directly under 
the future front wall of the furnace. 

This is arched over with two 4-inch courses of red brick, upon 
which come one or two 4£-inch courses of fire-brick. The bridge 
wall and two lateral walls of the ash-pit are also begun from the 
same level. It is also well to carry up the side and front walls 
of the furnace from the very bottom, using red brick for all 
underground work, and filling the space between and outside of 
the walls with stone or slag, broken in situ with spalling-ham¬ 
mers, and firmly united with liquid mortar, or by pouring in the 
pots of slag as they come from the blast-furnace. 

It is quite customary to fasten the looped tie-rods for the 
perpendicular buckstaves by merely bending a hook at the end 
of the rod and building it into the wall, trusting to the weight of 
the superincumbent mason-work to prevent their drawing out. 
It is a much safer plan to introduce the tie-rods at a lower level, 
giving them sufficient length and inclination to pierce one of the 
central longitudinal walls, and providing each with an eye 
through which passes a long continuous bar of iron, which thus 
firmly holds all the tie-rods belonging to one side of the main 
body of the furnace. This bar is fastened to its fellow of the 
other side by a few short cross-rods, and the lower set of loops is 
thus firmly held in place, and far below any chance of being 
melted in two—an accident that would certainly occur in the 
course of time if they crossed the entire furnace above the sub¬ 
terranean arch. 

The inclosing walls of the furnace having been built to within 


REVERBERATORY FURNACES. 


301 


a foot of the floor surface, the hearth proper of the furnace is 
laid in the shape of an inverted arch, its lowest point in the 
center being in contact with the upper convex surface of the 
4-foot subterranean arch, while its sides rise at the rate of about 
half an inch to the foot. It is also slightly arched longitudinally, 
and should be well keyed and grouted, as it is intended to be so 
constructed as to prevent the possibility of its being floated up 
by any breaking through of the molten contents of the sand- 
earth. 

The hearth is now inclosed by side-walls of fire-brick, 44 inches 
thick, which support the arch when the proper height is reached. 
These are incased by strengthening walls of red brick, while they 
are protected on the inside by a 9-inch lining of fire-brick, which 
can thus be renewed when necessary without interfering with 
the arch. 

As the hearth is an elongated oval, narrowing to about 18 
inches at the skimming-door, while the external shape is usually 
that of a rectangle, it follows that the four exterior corners con¬ 
sist of useless pillars of rubble or brick-work. These are some¬ 
times avoided by conforming the external shape to that of the 
hearth, and inclosing the fire-brick with thin wrought-iron plates, 
or thicker plates of cast iron, often perforated with rows of holes 
to diminish their weight. The latter arrangement causes some 
difficulty in placing the buckstaves, and presents no decided 
advantage over the older plan of inclosing the hearth in a rec¬ 
tangular mass of brick-work, only 4 inches thick at the widest 
portion of the hearth, and increasing rapidly toward each 
extremity. Two heavy vertical cast-iron plates support the 
hearth at each end—the u conker-plate ” giving strength to the 
bridge-wall, while the front plate is placed just below the front 
door, the narrow horizontal skimming-plate resting upon it, and 
determining the eventual thickness of the sand-bottom. 

The bridge-wall is a massive structure of fire-brick, perforated 
by an air-passage about 3 inches by 10 inches, which has the 
conker-plate for its anterior wall, while a lighter easting forms 
its posterior boundary. A large blow-hole, or opening for the 
admission of air, should be left on each side of the furnace in the 
angle formed by the posterior wall of the main portion of the 
structure and the wall of the fire-box. These orifices are used 
only when an oxidizing atmosphere is desired, as in the concern 


302 MODERN AMERICAN METHODS OF COPPER SMELTING. 


tration of matte, the making of blister copper, etc., and can be 
tightly closed with clay under ordinary circumstances. 

The fire-box is inclosed with a 9-inch wall of fire-brick, which 
may be strengthened by a casing of common brick, if desired. 

Where coal is used for fuel, particular attention should be 
given to placing the grating-holes (that is, the orifices in the sides 
of the fire-box just above the grate, through which bars are intro¬ 
duced to cut away the clinkers) in a convenient position. 

The arch is best constructed of “ Dinas ” or silica brick, which 
last much longer than ordinary fire-brick, and should have a rise 
of an inch to the foot, pitching downward quite abruptly from a 
point slightly anterior to the bridge-wall, until it approaches to 
within twelve or fourteen inches of the skimming-plate at the 
front door. Its shape, as well as the size and proportions of the 
space between bridge and roof, has much to do with the heating 
qualities of the furnace, and must vary with the character of the 
fuel and with other local conditions. The extreme front row of 
arch bricks, forming the posterior wall of the flue opening in the 
roof, is called the “ vulcatory,” and from its situation is so ex¬ 
posed to wear and heat as to require frequent renewal. 

The flue opening itself is of a trapezodial form, being inclosed 
laterally between the two converging walls of the hearth, while 
it has the vulcatory for its posterior and the front wall of the 
furnace for its anterior boundary. 


Its size and proportions are matters of paramount importance, 
as the heating capacity of the furnace as well as its consumption 
of fuel depends principally upon it and upon the size and shape 
of the flue proper, that is, the canal connecting the hearth with 

the chimney. 

•/ 

No precise rules can be laid down in this matter for the guid¬ 
ance of the inexperienced, as each individual case must be judged 
upon its own merits until constant experimenting lias determined 
the question. 


The uncertainty and difficulty pertaining to this matter may 
be best appreciated when it is known that, of half a dozen fur¬ 
naces in the same building, constructed from the same plan and 
apparently identical in every particular, fed with the same fuel, 
and smelting the same ore, no two behave in the same manner, 
and therefore each must have the size and shape of its flue 
suited to its needs. In general terms, it may be stated that a 


REVERBERATORY FURNACES. 


303 


large flue will cause a greater consumption of fuel and a quicker 
heat, unless a certain limit is over-stepped, beyond which the 
fuel will be burned without a corresponding rise of temperature. 
It is quite obvious, therefore, that the economical smelter will 
seek to throttle his flue to the greatest possible extent compatible 
with the rapid production of the required temperature. The flue 
should be narrowest at its junction with the furnace, and expand 
considerably as it enters the stack, having at least 50 per cent, 
greater area at the latter point than at the former. Its size is 
altered by introducing or removing a little dam of sand at the 
end nearest the furnace, one of the slabs with which it is covered 
being removed for that purpose. When experiments of this 
nature are executed to determine the most advantageous flue 
area, it is important that the change in size should be sufficient 
to produce some plainly marked effect either for the better or the 
worse ; otherwise, it is a mere groping in the dark. The weather, 
force or direction of the wind, and general condition of the at¬ 
mosphere may often produce an impression sufficiently powerful 
to entirely mask the changes brought about by the alteration 
of the flue area, so that a considerable period may be necessary 
to properly estimate the good or evil resulting from the efforts of 
the smelter.* 

The buckstaves supporting the furnace should be of wrouglit- 
iron, and sufficiently strong and numerous effectually to prevent 
any spreading of the sides or arch. 

This is especially important with blister or refining-furnaces, 
where the weight of the molten bath may amount to 10 or 15 
tons, which, combined with the lateral pressure caused by the 
high temperature, produces an expansive force that is almost 
incredible. 

The tie-rods should be of lj-inch square iron, provided at the 
extremities with loops, and not with thread and nut. 

Where wood is used as a fuel, a row of small openings should 
be left in the arch over the anterior edge of the fire-bridge; an 
arrangement that insures the combustion of the gases in the 
hearth where they are needed, instead of in the chimney, where 

* The proportions of numerous reverberatory furnaces are given in Egles- 
ton’s monograph on Copper Refining in the United States, as well as in a val¬ 
uable paper by H. M. Howe, E. M., in the government report edited by 
Albert Williams, Jr. 




304 MODERN AMERICAN METHODS OF COPPER SMELTING. 


I 


they may produce a most detrimental effect, destroying the fire¬ 
brick lining within a few days. 

Even with this precaution, it is sometimes necessary to leave 
an opening near the base of the stack, to prevent excessive flam¬ 
ing just after adding fresh fuel. 

A damper playing in a hinge, and fastened to a cast-iron 
frame, should invariably be placed on the summit of the stack. 
By this means, the draught can lie effectually regulated, or en¬ 
tirely cut off if desired—as when charging fine, dry ore—without 
resorting to the familiar but slovenly practice of removing a slab 
from the flue and inserting an iron plate. 

The capacity of a reverberatory furnace and that quality of 
rapid, fierce heating so essential to economical ore smelting, are 
largely dependent upon the proportions of the flue and stack, 
and while the former may easily be made too large for econom¬ 
ical work, the latter is oftener too small for the sharp draught 
required. 


These remarks apply especially to reverberatories used for 
smelting ore, where the object is to attain the highest possible 
temperature in the shortest time. Blister furnaces, or those 
devoted to matte concentration by the old method of u sweating 
down/ 7 do not require such a powerful draught, as the processes 
are slow, and the temperature required comparatively low. For 
this reason, they may lie provided with down-takes and flues 
entering a stack common to several furnaces; while each ore- 
smelting reverberatory should have its own independent stack, 
without either flue or dust-chambers; any loss in flue-dust that 
may occur after closing the damper while charging being fully 
counterbalanced by the saving in time and fuel, except under 
peculiar circumstances. 

The fire-brick lining should be entirely independent of its sur¬ 
rounding walls, so that it can be easily removed and renewed, 
and a 2-inch air-space should be left between the same, connect¬ 
ing with openings near the base, so that a current of cool air 
may constantly surround the heated lining. 

As has been already mentioned, that portion of the stack be¬ 
low the entrance of the lateral flue should be left entirely empty 
nearly to the ground level, in order that an elastic cushion mav 
be provided for the flame as it enters the stack from the furnace. 

The height of the stack need seldom exceed 60 feet, unless. 


305 


REVERBERATORY FURNACES. 


local conditions affect the draught. The immediate proximity of 
higher roofs or abrupt hills often injures the draught to a most 
serious extent, which circumstance should always be borne in 
mind in planning new works. 

From a stack 65 feet high, the writer has removed 15 feet r 
and subsequently added 30 feet, without affecting the working 
of the furnace in the slightest degree ; but the height just men¬ 
tioned may be regarded as safe under ordinarv circumstances. 

The position of the large doors and other openings of the 
building should be so arranged that under no conditions can the 
wind blow across the ash-pit of the furnace in such a manner as 
to counteract the draught. It is not uncommon to find furnaces 
that, during certain winds and other atmospheric influences, fall 
off to a very marked degree in their duty. 

There should be an ample free space about a reverberatory 
furnace; at least 15 feet on the tapping side, and the same dis¬ 
tance in front, while a space of 12 feet on the charging-door side 
will suffice. This should be well drained and paved with brick 
on edge, or with cast-iron plates. 

The arch being completed and the wooden pattern removed, 
the furnace is taken in charge by the smelter, who, with the 
blacksmith’s aid, proceeds to the proper tightening of the tie- 
rods; the side buckstaves having been already sufficiently drawn 
up to keep the arch in place. This process has been described 
in the chapter on Calcining Furnaces, and pesenets no peculiar¬ 
ities. The empty hearth should be covered with a 2-inch layer 
of fire-clay, to prevent adhesion of any metal that may possibly 
make its way through the sand bottoms. 

A small fire may be at once built on the surface of the clay 
stratum and in the ash-pit, and should be maintained for at lease 
four days, slightly raising the temperature, until, at the expiration 
of this time, a dark-red heat is attained, and the cessation of 
aqueous vapors from the side walls and subterranean arch shows 
that every particle of moisture is removed. 

The grate-bars are now placed in position—being mere rods 
of inch-square wrought-iron—and the fire, being shifted to its 
proper position, is gradually urged for twelve hours or more, 
until the whole interior is of a light-red heat. 

Then, and not until then, should the material for the smelting- 
hearth be introduced. 


306 MODERN AMERICAN METHODS OF COPPER SMELTING. 


This consists essentially of silica, and may he in the shape of 
well-washed beach sand, or crushed sandstone, or of pulver¬ 
ized quartz, first roasted in lumps and quenched while hot, to 
impart a high degree of brittleness and greatly facilitate its 
crushing. 

A beach sand employed for this purpose in Swansea, and 
analyzed by Percy, had the following composition: 


Per cent. 


Silica. 87*87 

Alumina. 2*13 

Sesquioxide of iron. 2*72 

Lime. 3*79 


Per cent. 


Magnesia. 0*21 

Carbonic acid and water. 2*60 

Total. 99*32 


This is not so refractory as the crushed sandstone employed 
by some of the Eastern American smelting-works, or the pulver¬ 
ized quartz used for reverberatory bottoms in Butte, Montana, 
which, according to the author’s tests, contain respectively, when 
dry, 95’3 per cent, and 97*2 per cent, of insoluble residue, pre¬ 
sumable silica. 

Two methods are pursued in making reverberatory hearths. 
Either the sand chosen contains enough bases to be slightly fusi¬ 
ble, or a small proportion of crushed slag or other similar sub¬ 
stance is added so that the sand may become slightly agglomerated 
bv the intense heat to which it is subjected; or secondlv. the 
material selected is practically infusible, and the cementation of 
its particles is effected by smelting small and repeated charges 
of fusible material upon the slightly hardened surface of the 
s une, until it is solidified into a hard and impermeable mass. 

The author prefers a combination of these two systems, using 
the first method for the lower hearth, and the second for the 
upper or true hearth • as it is usual to put in two separate hearths, 
the upper one being comparatively thin, so that it can be easily 
removed when worn out. 

The total height from the floor of the furnace to the upper 
surface of the skim-plate being perhaps 30 inches, the lower 
hearth (including the clay bottom) should have a thickness of 18 
inches and the upper of 12 inches, both of them being somewhat 
concave in shape, so that a basin is formrd some 5 inches deeper 
than the skim-plate in the center, and sloping from every direc¬ 
tion toward the tap-hole. 

The size of the hearth material is a matter of less importance 











REVERBERATORY FURNACES. 307 

than is often supposed, provided that, if at all coarse, sufficient 
fine dnst is present to fill all interstices and prevent porosity. 

If good crushing facilities can be had, it is well to pass every¬ 
thing through a lG-mesh screen, but the author has used even a 
5-mesh without evil results. 

This, of course, refers to sandstone or quartz rock. Natural 
sand usually requires no sizing process, unless mixed with gravel. 

The utmost care should be taken to prevent the introduction 
of any foreign material, especially of an organic nature, as the 
gases generated therefrom may easily cause a ruinous flaw or 
blister in an otherwise perfect hearth. 

Such unfortunate results, however, are usually counteracted 
by the thorough calcination that all sand must undergo previous 
to the final smelting. 

A sufficient amount of the sand—usuallv from 4 to 5 tons— 
being thrown into the heated furnace (either as such, or mixed 
with from 3 to 5 per cent, of pulverized slag), a moderate fire is 
maintained, while a steady stirring and rabbling is kept up 
through the side and front doors, until every particle of moisture 
and carbonic acid and other gases is expelled, and the heat grad¬ 
ually raised to such a temperature as to insure the decomposition 
of all organic material. This operation may require from 3 to 8 
hours, according to the nature of the material. Both the temper¬ 
ature and time are matters of great importance, having a marked 
effect upon the final result; but can only be learned by experi¬ 
ence, as they vary with each different sand. 

Toward the close of this period, the sand is gradually brought 
into the proper shape for the bottom, and thoroughly pressed 
and stamped into place by means of long paddles and stampers, 
worked through the door openings. No great pains need be 
expended upon the lower hearth, as it will, of course, be entirely 
covered and its shape obliterated by the superior layer. 

The doors are then closed; the tap-hole bricked up and cov¬ 
ered with a heap of sand, and every crack and orifice about the 
whole furnace completely stopped and closed. The fire is grad¬ 
ually urged until the highest possible temperature is reached and 
maintained for a couple of hours, the entire period of heating 
requiring from G to 14 hours, according to the heating capacity 
of furnace and fuel. The interior condition of affairs is watched 
through a peep-hole in the front door, which is provided with a 


308 MODERN AMERICAN METHODS OF COPPER SMELTING. 


clay plug. After a proper maintenance of the highest temper¬ 
ature, the fire is gradually slackened and the furnace cooled 
down. This operation demands the greatest care and circum¬ 
spection, as the premature opening of a door or a sudden draught 
of cold air may cause the appearance of a crack or blister in the 
porcelain-like surface of the sand hearth. Several hours must 
elapse before the doors can be taken down and the results of the 
operation inspected. The interior of a reverberatory furnace 
under these circumstances is quite an interesting sight. 

Long stalactites of molten fire-brick hang down from the arch 
over its entire surface. The side walls are not only glazed, but 
actually fused until they begin to soften to a considerable 
depth, and the hard and glistening semi-fused surface of the new 
hearth is strewn with fragments of brick from the crown, and 
little heaps of molten fire-clay corresponding to the pendent 
stalactites. 

LTnless very serious cracks exist, no notice need be taken of 
them, and blisters and irregularities may be entirely overlooked, 
as the upper hearth is to bear the brunt of the work. After slow 
and perfectly even cooling to a dark-red heat, about 1,800 pounds 
of moderately basic, fusible slag, crushed to the size of chestnuts, 
are spread over the entire surface, being charged by means of 
long-handled paddles, and on no account thrown in carelessly, to 
be subsequently leveled with rabbles, as is often done. The 
doors being again tightly closed, the slag-charge is quickly 
smelted down, two hours being amply sufficient for this purpose. 
This layer of slag will be entirely absorbed by the porous sand 
bottom, which, after a second cautious cooling, should be again 
charged with a somewhat larger burden of slag, with which are 
mixed a few hundred pounds of low-grade matte (30 per cent.). 
After this is melted down, a considerable portion will probably 
be found in a pool near the tap-hole, from which it should be 
immediately evacuated. If the furnace is to be used for concen¬ 
tration work, or especially for the production of blister copper, 
still another charge should be melted on the lower hearth, con¬ 
sisting principally of matte of the same grade as the former, and 
should be tapped as soon as sufficiently liquid. In this way, the 
lower hearth will be pretty thoroughly saturated with matte of 
low tenor, thus preventing the absorption of an equivalent quan- 


REVERBERATORY FURNACES. 


309 


tity of richer metal in case the same should penetrate from the 
upper hearth. The tying up of a large amount of copper may 
thus be guarded against. 

After a final cooling, the sand to form the upper hearth is 
thrown in, and, after a careful calcining and leveling, should be 
stamped into place with the utmost care, sloping gently toward 
the tap-hole from every point. 

The fusion is executed in the manner already described, and 
in addition a careful watch should be maintained at the peep¬ 
hole to observe and remove any fragments of brick that may fall 
from the arch during the early period of the fusion. After the 
softening of the sand has once begun, no further manipulation is 
permissible. 

The cooling after the fusion must be executed with extreme 
care, to prevent cracking and blistering, and as soon as a dull- 
red heat is reached, the slag and matte charges already enu¬ 
merated should be successively melted, with alternate periods of 
cooling. 

As a final preparation before introducing the first ore-charge, 
a small quantity of finely crushed slag should be thrown around 
the entire edge of the hearth at the junction of sand and fire¬ 
brick. 

Above this, a thick bolster of “fettling” (mixed fire-clay and 
crushed quartz) should be tightly forced into the angle between 
hearth and side-walls, including the bridge-wall. 

An hour’s brisk heat will dry and consolidate the fettling, and 
the regular work of the furnace may begin—small charges being 
used at first, and no large quantity of metal allowed to accumu¬ 
late before tapping. 

MANAGEMENT OF FURNACE. 

The experienced furnace-man constantly watches his furnace 
with reference to the safety and condition of its bottom. After 
a few hours’ firing on a fresh charge, the workman introduces 
his rabble, and by the feeling of the sand when gliding over the 
bottom, determines at once the condition of things. 

If slippery and sticky, it indicates that portions of the charge 
still adhere to the hearth. These are removed as far as possible 
by the rabble, and dissolved by a short additional heat, until the 


310 MODERN AMERICAN METHODS OF COPPER SMELTING. 

rabble glides smoothly over a plane/granular bottom, which is 
the upper surface of the liearth proper. After this condition is 
once attained, every additional moment of high temperature 
is not only wasted, but is positively detrimental to the hearth, 
which lacks the protection of the semi-fused ore, the liquid matte 
soon attaining a high temperature, and, if exposed to the air, 
boiling in a manner that may prove highly dangerous to the bot¬ 
tom. This is the case when concentrating matte or making 
blister copper—operations very severe on the bottom, but ren¬ 
dered less dangerous by being conducted at a lower temperature 
than is required for smelting proper. 

Equally detrimental may be a high temperature with a small 
charge, where the unprotected portions of the bottom may be¬ 
come so softened as to rise in large flakes, being literally floated 
up by the superincumbent metal. 

Any large piece of iron, such as a rabble-head, may cause a 
hole in the bottom, and in endeavoring to float up an old bottom, 
nothing is more effective than the introduction of a number of 
large fragments of old iron. A bottom may be often patched to 
advantage when only locally damaged. When any such condi¬ 
tion is discovered, the hearth should be immediately emptied, 
and the damaged portion, which usually shows a decided cavity 
or depression, should be most carefully emptied, fresh sand being 
repeatedly introduced and again removed with the rabble until it 
is completely dry. The hole should then be filled and leveled up 
with ordinary bottom sand, which must be fused and saturated 
with the same precautions as in the case of the original bottom. 
In this way, a bottom may often be saved for many months at a 
very slight expense. 

In direct connection with the management of the bottom is 
the proper fettling of the furnace. The entire life of the side 
walls and safety of the bottom depend upon the care and con¬ 
scientiousness observed in maintaining the dam that incloses the 
molten, liquid pool and protects the fire-brick. In default of this 
safeguard, the side walls are quickly undermined, a groove several 
inches in depth being cut into the mason-work during the smelt¬ 
ing of a single basic charge. Nothing then remains to prevent 
the descent of the metal between the wall and bottom until the 
latter is floated up and ruined, and a large amount of copper 


REVERBERATORY FURNACES. 


311 


•temporarily lost. The best fettling is formed of pure, white 
quartz, crushed through a 3-mesh screen and mixed with sufficient 
plastic fire-clay to form balls, which may be placed at exactly the 
required point, and forcibly pressed and molded into place. The 
quartz may be replaced by ordinary bottom sand, which, however, 
is less permanent and solid. When smelting basic ore, the hearth 
may require fettling after every charge; but with a quartzose 
mixture, days may elapse without any necessity for renewal. 
Safety in this particular is only obtained at the expense of con¬ 
stant watchfulness. 

The size of the fire-box and depth of grate below the upper 
surface of the bridge are very variable factors,' depending upon 
the quality of the fuel and degree of temperature. 

The best and most economical results are obtained by the use 
of the clinker grate, which is virtually a gas generator, a deep 
layer of clinkers being maintained upon the grate-bars, penetrated 
by numerous openings through which the air passes, being heated 
to a high temperature before it unites with the gas generated 
from the coal, which lies upon the upper surface of the bed. A 
certain proportion—from one-third to one-half—of caking coal 
is required for this method of combustion, and the grate-bars 
must be at a much greater depth than for ordinary non-caking 
fuel. 

Lignites, or any free-burning, non-caking coal, require a shal¬ 
low grate and a large flue, while wood behaves in much the same 
manner, requiring, however, the introduction of air through holes 
in the roof above the bridge, on account of the great volume of 
combustible gases generated. 

It is almost impossible to give any general rule for the amount 
of fuel required for a reverberatory furnace. When engaged in 
smelting ores, a much larger quantity must be consumed than 
in making blister copper or in the refining process, where only a 
very moderate temperature is needed for a considerable portion 
of the time. The following table gives the average results ob¬ 
tained by the writer, and comprises several varieties of fuel, and 
most of the different operations executed in the reverberatory 
furnace: 


312 MODERN AMERICAN METHODS OF COPPER SMELTING 1 . 


TABLE OF REVERBERATORY WORK. 


Operation. 

Fuel. 

Size of fire-box 
in feet. 

Size of hearth. 

Fuel used per 
twenty-four 
hours. 

Ore smelting... 

Lignite. 

34 X 4 

9 x 144 

54 tons 

Same furnace.. 

Bituminous 

coal. 

34 X 4 

9 x 144 

3f tons 

Same furnace.. 

Wood. 

34 x 4 

9 x 144 

64 cords 

Ore smelting... 

Bituminous 

coal. 

34 x 4 

10 x 15 

3| tons 

Blister smelt¬ 
ing. 

Bituminous 

coal. 

34 x 4 

10 x 15 

24 tons 

Blister smelt¬ 
ing. 

Wood. 

34 x 4. 

10 x 15 

4f cords 

Refining. 

Wood. 

3f x 44 

9 x 134 

5 “ 

Refining. 

Coal. 

34 x 4 

94 x 14 

3 tons 


One ton = 2,000 pounds. 

Anthracite may be employed in this form of furnace, when provided with, 
a tight fire-box and an artificial blast of considerable volume and slight 
pressure. 


ESTIMATE OF LABOR AND MATERIALS FOR BUILDING AN ORDINARY 

REVERBERATORY FURNACE. 

Size of hearth inside, 9J by 14 feet. Besides the independent 
9-in lining of fire-brick, inclosing the hearth; there is a backing 
of 4J inches of fire-brick, from which the arch takes its spring, 
and a casing of red brick, 12 inches thick at the yddest part of 
the hearth, and rapidly increasing in thickness toward either 
end. The fire-box is 34 by 4 feet, and the bridge 30 inches across. 

All these, as well as the remaining proportions, may be altered 
within ordinary limits, without materially affecting this estimate. 

Detailed drawings of the best modern reverberatories will be 
found in a succeeding section. 


EXCAVATION FOR FOUNDATIONS. 

This should be about 18 inches larger in every direction than 
the proposed stone foundations, and about 3 feet 9 inches deep 
ordinarily, while the excavation for the stack-foundation is put 
at 6 feet deep. The amount of earth usually removed is about 
1,940 cubic feet, costing, to dig and remove, about 2J cents per 
cubic foot. Total, $48.50. 




















REVERBERATORY FURNACES. 


313 


STONE WORK. 

The stone foundation walls are usually continued to within 
about 8 inches of the surface of the ground, and will require 
about 700 cubic feet of stone work, which includes the stack- 
foundation complete at 35 cents per cubic feet. Total, $245.00. 

BRICK WORK. 

The fire-brick required will be : Cubic feet. 

For lowest fire-brick arch over four-foot vault. 25 . 

Main concave arch, forming bottom. 114 

Front wall at skimming-door. 6 

Flue and covering slabs... 22 

Bridge-wall, estimated as if solid. 35 

Two side walls of fire-box. 110 

Rear wall of fire-box. 15 

Hearth lining. 100 

Lining of stack, estimated at 14 inches thick for lower 
half and 4^ inches for upper half, stack 60 feet high, 
and assumed to be 32 inches square iu the clear 
throughout, to simplify calculation. 690 

Total cubic feet. 1,117 

Assuming 18 fire-bricks to the cubic foot, we have a total of 
square fire-brick of 20,106. To these must be added the follow¬ 
ing so-called u shaped brick,” to avoid cutting in turning arches, 
door-jambs, etc., and in laying skew-backs. 

No. of brick. 

Bull-heads. 250 

Side skew-backs. 250 

Jamb-brick. 60 

Wedge brick. 30 

Soaps. 80 

Splits. 80 

Total. 750 

Added to the square brick = grand total.20,856 

Say 21,000 at $40 per thousand.$840.00 

The main arch of the furnace will require 2,000 Dinas 
brick at $60 per thousand.$120.00 

FIRE-CLAY. 

For laying the above brick will be required: 

Raw fire-clay, 5 tons at $8. $40.00 

Burnt fire-clay, 5 tons at $8..•. 40.00 


$80.00 



























314 MODERN AMERICAN METHODS OF COPPER SMELTING. 


10 loads at $2 


ORDINARY CLAY. 


$20.00 


The red brick required are : 

For side walls of vault under furnace... 
For double 4-inch arches over vault.... 

Front wall under skim-door. 

Side casing walls and solid corners. 

Side casing walls of fire-box and ash-pit 


Cubic feeu 
192 
43 
84 
408 
128 


855 


Casing of 50-foot stack, assuming it to average 12 inches 

thick for the entire distance. 1,260 


Grand total. 2,115 

Assuming 25 brick per cubic foot—to allow for waste, 
we have total number of red brick, 52,875—say 53,000 
at $8. $424.00 


LIME, SAND, AND CEMENT. 

To lay the above brick requires : 


50 barrels lime at $1. $50.00 

12 barrels cement at $1.50. 18.00 

.25 loads sand. 36.50 


Total 


$104.50 


IRON WORK. 

Assuming that no proper expense is to be spared, the follow¬ 
ing iron work is required, being somewhat heavier than is com¬ 
monly used, though no more than is needed for a strong and 
permanent furnace. Most of these plates are ribbed to increase 
their strength. 

Bridge plate, 5 feet long, 32 inches high, 3 inches thick, Pounds. 


tapered and cored with holes to lessen weight. 1,120 

Front plate (across entire front and below skimming- 
door), 6 feet 3 inches long, 2 feet high, 3 inches thick, 

tapered and perforated. 1,110 

Ribbed plate to support rear wall of fire-box, 5 feet long, 

9 inches wide, 1 inch thick, with heavy rib on top.... 182 


Ribbed plate to support the fire-box portion of bridge- 

wall, 5 feet long, 9 inches wide, 14 inches thick. 246 

Rear bridge-plate, which forms rear wall of air channel 
through bridge, 5 feet long, 2 feet 8 inches high, and 


2 inches thick (tapering). 500 

Plate to support one end of fire-box and contains frame 
for sliding door, 32 inches wide, 36 inches high, 1 inch 
thick. 200 


Carried forward. 3,358 
























REVERBERATORY FURNACES. 


315 


Brought forward. 3,358 

Skimming-block, forming threshold of skimming-door, 
and easily removable, 26 inches long, 8 inches wide on 
top and 5 inches below, and 10 inches high. 430 


Plate to protect brick-work at side-door with opening for 

door, 6 feet 9 inches long, 5 feet high, f inch thick... . 725 

4 skew-back plates on main furnace, above and below, 
each 17 feet long, 4 inches wide, 1 inch thick, with 


heavy rib. 

Plate to support flue, 3 feet long, 24 inches wide, 1 inch 

thick, with light ribs. 

Chimney cap and damper. 

Frames for fire-door and charging-door... 

2 bearing bars for grates and 1 grating bar, 5 feet long 
and 2 by 3 inches wide. 


Total cast-iron for reverberatory furnace... 

WROUGHT-IRON. 

Tie-rods of 1£ inches round iron. 

9 upper and 9 lower across main part of furnace.. 

3 upper across fire-box. 

2 upper longest. 

2 upper longitudinal on main furnace. 

2 upper uniting in ring. 

7 lower hooks in fire-box. 

2 lower hooks at end of fire-box. 

2 lower hooks at end of main furnace corner. 

6 lower hooks in front. 

52 loops for above to go over buckstaves. 

30 loops to connect irons across vault. 


Feet. 

252 

24 

45 

34 

16 

18 

12 

10 

30 

156 

90 


1,061 

246 

549 

181 

305 

6,855 

Pounds. 


687 = 2,900 


Grate-bars, 24 of inch square, 4 feet 3 inches. 345 

Arcs, levers, and chains for fire-door and charging-door.. 92 

Skimming-bar, 6 feet long, f inch by 2 inches. 26 

Bolts and nuts about furnace. 72 

Clamps for flue-slabs and brick doors. 54 

Chain to damper. 14 


Total, except old rails. 3,503. 

Buckstaves, old rails, 90 pounds to the yard. 

9 for each side of main furnace, at 6£ feet. 117 

5 for both sides of fire-box, at 6| feet. 33 

2 long at rear end of fire-box, at 9 feet. 18 

2 at main end corners, at 6 feet. 12 

6 at front of furnace, at 5 feet. 30 

2 light ones for fire-door. 6 

© 


2 longitudinal rails under vault to connect irons 
from each side, at 16 feet. 


% 


248 = 7,440 





































316 MODERN AMERICAN METHODS OF COPPER SMELTING. 


WROUGHT-IRON FOR CORNERS OF STACK. 


480 feet of | inch by f inch iron for uprights. 605 

360 feet $ inch by If inch iron for cross straps. 532 

Total. 1,137 

RESUME OF IRON WORK. 

Cast-iron, 6,855 pounds at 2£ cents. $171.36 

Wrought-iron, 4,640 pounds at 2 cents. 92.80 

Old rails. 56.04 


$320.20 

LUMBER. 

Lumber for main furnace arch, foundation arch, and 


chimney scaffolding, 2,360 feet at $18. $42.48 

LABOR ON REVERBERATORY, EXCEPTING FOUNDATIONS. 

Mason’s labor, 160 days at $4.00. $640.00 

Helper’s labor, 165 days at $2.00. 330.00 

Carpenter’s labor, 9 days at $3.00. 27.00 

Blacksmith and helper’s labor, 84 days at $5.00. 42.50 

Ordinary labor, 35 days at $1.50. 52.50 

Grading and clearing up. 66.00 

Superintendence. 124.00 

Incidentals. 37.00 


Total labor. $1,319.00 

SUMMARY OF TOTALS. 

Excavation. $48.50 

Stone-work. 245.00 

Fire-brick. 840.00 

Dinas brick. 120.00 

Fire-clay. 80.00 

Ordinary clay. 20.00 

Redbrick. 424.00 

Lime, sand, and cement. 104.50 

Ironwork. 3 () 0 °0 

Lumber. 4° 48 

Labor, superintendence, etc. 1,319.00 


Grand total. $3,563.68 


TOOLS. 

The tools for a reverberatory smelting furnace should em¬ 
brace : 

1 long and 1 short paddle. 

4 ordinary skimming rabbles. 

6 ordinary stirring rabbles. 


































REVERBERATORY FURNACES. 


317 


2 long stirring rabbles. 

2 long clay stampers (for repairing). 

2 short clay stampers (for repairing). 

4 steel tapping-bars. 

1 striking hammer. 

1 sledge-hammer. 

4 steel grating-bars, assorted lengths. 

1 coal shovel. 

Ordinary shovels. 

1 rake. 

1 iron wheelbarrow. 

1 slag barrow. 

Various hooks, pokers, etc. 

Weighing in the aggregate (excepting barrows, shovels, and 
such tools), iron, about 1,300 pounds; steel, about 275 pounds. 

All rabbles and bars are made and repaired at the furnace, 
the heads of the former being usually imported from England, 
and welded to the wrought-iron bar. 

ESTIMATE OF COST OF RUNNING A REVERBERATORY FURNACE. 

It is assumed that coal, ore, and fettling materials are of good 
average quality, and that the cost of superintendence and similar 
expenses is divided among six furnaces. The helpers of neigh¬ 
boring furnaces assist each other in charging and removing slag. 

The allowance for repairs, as well as all the figures given, may 
be taken as reliable under the conditions assumed, as they are 
the average results of a year’s actual work. 

The cost of preparing and smelting in the two sand bottoms 
is also given, the figures adopted being the average of nine such 
operations, and consequently including such mishaps as will 
occasionally occur. 

The general expenses of the works are too variable to be 
properly considered in such an estimate. The same may be said 


regarding fluxes. 

COST OF REVERBERATORY FURNACE BOTTOM. 

—Lower Bottom. 

Fire-sand (or prepared quartz), 4‘75 tons at $8. $38.00 

Coal for preliminary heating and fusion, 6‘5 tons at $5 32.50 

Two smelters at $3 (24 hours’ operation). 6.00 

Two helpers at $2... 4.00 


Carried forward. $80.50 







318 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Brought forward. $80.50' 

One laborer. 1.50' 

Proportion of coal transportation. .25 

Proportion of 2 foremen at $4 each. 1.33 

Lights, oil, soap, etc. .65 

Repairs on furnace tools. .60 

Clay and sand for doors, tap-hole, etc. .15 


Total. $84.98 

B — Upper Bottom . 

Fire-sand (or prepared quartz), 3‘9 tons at $8. $31.20 

Coal for sand-roasting and fusion, 5‘2 tons at $5. 26.00 

Two smelters at $3. 6.00 

Two helpers at $2. 4.00 

Two laborers at $1.50. 3.00- 

Transportation of slag and matte to soak bottom. .85 

Proportion of coal transportation. .20 

Proportion of 2 foremen at $4 each. 1.33 

Clay and sand for final fettling, doors, tap-hole, etc.. 1.60 

Lights, oil, soap, etc. .65 

Repairs on furnace tools. .75 


Total. $75.58 

Grand total. $160.56 

COST OF RUNNING REVERBERATORY SMELTING FURNACE 24 HOURS. 

Coal, 4‘3 tons bituminous coal at $5. $21.50 

Clay and sand for fettling, 220 pounds. .45 

Cheap clay and loam for luting; sand for matte beds, 

800 pounds.*. .60 

Proportion of renewing upper bottom annually.24 

Proportion of renewing main arch annually.69 

Proportion of renewing flue quarterly. .21 

Proportion of other repairs of furnace. 88 

For renewing tools and barrows. 1.36 

Repairs on tools and barrows. 1.25 

Lights, oil, soap, chalk, etc. .72 

Refuse wood for drying matte beds (only happens ex¬ 
ceptionally). X 2 

Repairs on furnace doors. .13 

Two smelters at $3. 6.00 

Two helpers at $2 . 4 60 

One laborer (on day shift only). 1.50 

Proportion of coal transportation. .25 

Proportion of ore transportation. 40 

Proportion of selecting slag and building dump.25 

Proportion of removing ashes. .25 

Proportion of 2 foremen (day and night) at $4 each.... 1.33 

Allowance for extra help (exceptionally). .33 


$42.46 













































REVERBERATORY FURNACES. 


319 


As such a furnace should easily smelt 12 tons per twenty-four 
hours of favorable ores, the cost per ton would be $3.54, which sum 
will be augmented by a certain proportion of the general expenses, 
as well as by whatever duxes may be found necessary to add. 

Where iron is cheap, the entire furnace is frequently inclosed 
in wrought or cast plates of that metal, the latter being usually 
seven-eighths inch thick and closely perforated with niche holes, 
cored out in the casting, to lessen the weight of the plates. 

When thus supported, the exterior red brick casing may be 
omitted, as well as the massive corners, thus giving the main 
body of the furnace a coffin shape. This is the case with the 
reverberatories of the Orford Copper and Sulphur Company con¬ 
structed by H. M. Howe. 

t/ 

ORE SMELTING FOR COARSE METAL* 

This operation requires the highest attainable liea-t in the 
shortest possible time. The furnace, therefore, should have a 
comparatively large dre-box and due, and also a hearth of the 
largest practical dimensions, in order to contain a sufdcient 
charge of the light and bulky ore. 

Beginning with the old Swansea standard of 9 or 91 feet width 
of hearth, the author has seen this gradually enlarged to 11 feet, 
without increasing the size of the fire-box (3J by 4 feet) or the 
consumption of fuel, and raising the capacity of the furnace 
from 2 or 21 tons per charge to 3| or 4$, the time of fusion in 
both cases being identical; that is, from 41 to 7 hours, according 
to quality of fuel and fusibility of charge. 

Including delays, waste of time in charging, tapping, etc., 4 
charges per day of 4 tons each may be considered good average 
work for calcined ores of reasonable fusibility, when the metal 
produced does not exceed 40 per cent, in copper. The produc¬ 
tion of a richer matte lengthens the period of fusion for several 
reasons. 

Among these is the fact that rich matte does not possess the 
power belonging to low-grade metal, of rapidly floating up and 
detaching the semi-fused masses of ore from the furnace bottom, 
and thus shortening the process. Rich matte also presupposes 
a quite thorough calcination, so that there is not only a less pro- 

* See paragraph entitled “Improvements in Reverberatory Smelting” 
for the latest results. 




320 MODERN AMERICAN METHODS OF COPPER SMELTING. 


portion of easily fusible sulphides, but much of the sulphide of 
iron present has been changed into ferric, instead of ferrous, 
oxide, which is nearly infusible, and must be for the most part 
reduced to the lower oxide before it can combine with silica. 

For these reasons, and more especially for fear of producing 
too rich a slag, the Swansea custom has forbidden the production 
of a matte from the first fusion of above 35 per cent, copper. 
The presence of arsenic and antimony, which require for their 
removal a long series of alternate oxidations and reductions, also 
has favored this practice 5 but with our purer and richer native 
ores, and with the high prices of fuel and labor, it has become the 
custom to produce a much higher grade of matte at the first fusion. 

This also is the practice in Chili, where the first matte ap¬ 
proaches 50 per cent. 

Long experience in the practice of making a first rich matte 
has resulted in divesting it of many imaginary as well as real 
disadvantages. The following pages will show to what an ex¬ 
treme it has been pushed, where local conditions combine to 
render it advantageous. 

The very high prices of labor and material at Butte, Montana, 
and the comparative cheapness of high-grade ores of copper, 
render that metal, while in the ore, about the cheapest thing 
there; so that it is much more profitable to sacrifice a small por¬ 
tion of copper than to attempt to save it all at the expense of 
fuel and labor. 

Nor need the loss of copper in the slags from even the highest 


grade metal lie as great as is often supposed. 

The following results of work executed at the furnaces of the 
Parrot Copper Company, of Butte, Montana, illustrate, as has 
been said, the extreme practice of this kind. The assavs were 
made by the company’s chemist, Mr. I). P. Murphy. 

Each assay represents a shipment of matte of from 15 to 16 
tons, while the slag samples are average results of each charm?. 


which could be 

extended to almost any desired limit. 


Assay of matte. 

Per cent, copper. 

G4-3. 

Assay of slag. 

Per cent copper. 

Assay of matte. 

Per cent, copper. 

61-8. 

Assay of slag. 
Per cent, copper. 

627. 


63-6. 


66-5. 


64-5. 


66 • 2. 


63-3. 


65*9., ... 


66-2. 















REVERBERATORY FURNACES. 


321 


One of the great secrets of rapid fusion, always assuming that 
the flue and chimney are of the proper size, and that the firing 
is managed with skill and regularity, is the absolute exclusion of 
all currents of ah* from the interior of the furnace. The chilling 
effect produced by even the slightest crack or orifice in the brick¬ 
work or from deficient claying up of the doors, would be incred¬ 
ible to the inexperienced. The front and side doors, made of 
fire-brick, inclosed in an iron frame, are fitted closely to the sides 
of the furnace surrounding the door openings, and all cracks 
luted with plastic clay. As the charge is usually too siliceous 
already, and as any addition of this clay, which is sure to fall 
down upon, and become mixed with, the ore charge, at the side 
door, is a decided detriment, the smelter uses the smallest prac¬ 
ticable quantity of the same. This shrinks on drying, permitting 
the ingress of air currents, which may have a most serious effect 
in retarding the process. 

The author has remedied this by substituting for the worthless 
clay the raw slimes from the settling-pits, where concentration 
is employed, or fine screenings from the roast-heaps where the 
former material cannot be procured. 

This may seem a small item, but the quantity of lute used is 
very great, as may be inferred from the fact that the substitution 
of the concentration slimes for clay in works containing six 
reverberatory furnaces effected an increased production of 1,000 
pounds of copper monthly at no expense, but with the saving of 
some $15 in clay. 

As the gangue of copper ore is usually quartzose, the rever¬ 
beratory smelter is seldom troubled with too basic a charge. 

Where this occurs, it is a decided evil; for although extremely 
fusible, it rapidly destroys the fettling and sand bottom, and, 
what is of far greater importance, produces so thin and fluid a 
slag that its removal from the metal by skimming is almost im¬ 
possible. In such instances, the only remedy is to allow the 
liquid charge to cool until the slag has stiffened sufficiently to 
render its removal less difficult, or to throw a considerable quan¬ 
tity of ashes or coke-dust over the surface of the bath, which acts 
in the same way. It is sometimes necessary, after skimming the 
principal portion of the slag, to allow the remainder to chill until 
it becomes so thick that, on tapping, it will remain in the fur¬ 
nace, while the more fusible matte is run into the ordinary sand 


322 MODERN AMERICAN METHODS OF COPPER SMELTING. 

molds. This is a misnomer, however, as sand would be the worst 
possible material for the construction of molds, a sandy loam 
being the proper substance, and being dampened only sufficiently 
to render its manipulation feasible. It must be thoroughly dried 
before tapping, to avoid explosions, especially when coarse metal 
(below 45 per cent.), which is peculiarly liable to this accident, is 
being made. The richer grades of matte may be run into quite 
damp molds with impunity. But special care must be taken 
with blister copper, which is more explosive even than the lower 
gi^ades of matte. If serious boiling of the liquid metal in the 
molds occurs, indicating a probable impending explosion, the 
spot should be at once covered with old boards, which should 
always be held in readiness. Any outbreak is controlled by dry 
sand, water being avoided in all cases. Fortunately, these dem¬ 
onstrations are less dangerous than they appear, and very few 
cases of explosion are so serious as to prevent the attendants 
from remaining in the building and protecting it from destruction 
by fire. A little pluck and plenty of dry sand will nearly always 
suffice to prevent any serious results. 

After the removal of the pigs of matte from the molds by the 
furnace-helper, assisted by a second man, the sand should be 
raked over with an iron rake, and all coarse pieces returned to 
the next charge. 

The pigs of slag from the slag-bed may be generally thrown 
over the dump, but the plate slag should be re-smelted entire, 
and every pig of slag, when cool, should be carefully examined 
for prills. 

It is more advantageous to charge a furnace by the side door 
than by the means of a hopper above the roof, as the proper 
leveling and distribution of the heavy charges now used are 
almost impracticable by means of the rabble, while, when charged 
with a shovel, every pound of ore can be thrown just where it is 
needed. In order that no time be wasted, the helpers from other 
furnaces assist in charging, at least four men being required. 
The work is exceedingly hot and laborious, as the entire process 
should be completed in from ten to fifteen minutes, to avoid 
waste of time and fuel. Later experience has shown that charg¬ 
ing can be done perfectly well from hoppers. 

The tapping of the metal should occur as seldom as possible, 
as the influence of the molten matte upon the fresh charge is 


REVERBERATORY FURNACES. 


323 


very favorable, arid prevents that persistent adherence to the bot¬ 
tom that is one of the chief causes of delay. 

*/ 

In case a charge should adhere in this manner, it is usually 
better to skim it as soon as a few hundredweight of clean slag 


can be obtained. If the direct contact of the flame for half an 
hour or more still fails to raise the old charge entirely, the work 
should not be unreasonably delayed, but the fresh charge should 
be distributed in such a manner as to leave bare those portions 
that adhere most closely, and which will usually be loosened by 
this double period of firing. 

Those portions of the hearth subject to the most excessive heat 
and wear, such as the bridge and side walls, should be thickly 
covered with ore, even to the extent, if necessary, of heaping 
three-fourtlis of the charge upon a comparatively limited area, if 
such practice be found conducive to the quickest fusion and 
greatest capacity. 

In charging a mixture composed of various ingredients, the 
succession in which they are thrown upon the hearth is by no 
means a matter of indifference. With a mixture of calcined 
pyrites (or matte), raw quartzose ore, and rich slag (a very com¬ 
mon charge), the calcined ore should be thrown upon the hearth, 
which it protects by its want of conductivity ; the quartzose ore 
should come next; while the very fusible slag should surmount 
the whole. In this way, want of conductivity of the calcined ore 
is prevented from delaying the fusion, as it would if it covered 
any of the other substances, and is made positively useful in pro¬ 
tecting the hearth. 

The size to which ore should be crushed for reverberatory 

«/ 

smelting depends upon its fusibility; very quartzose ore being 
benefited by passing a 4-mesh screen, while basic or sulphide ore 
may be of .almost any reasonable size. 

Very fine crushing should be avoided, on account of excessive 
formation of flue-dust as well as of its property of becoming so 
compact as to resist the highest temperature. 

After fusing any calcined ferruginous material for several days, 
the hearth will be found covered with slimy masses of reduced 
iron, which, to a certain extent, may be beneficial as a protection 
to the bottom, but when beyond a certain limit, must be removed 
by persistent firing, assisted, when necessary, by a small charge 
,of raw. sulphurets, which will rapidly float up and dissolve the 


324 MODERN AMERICAN METHODS OF COPPER SMELTING. 


accretions. Several thousand pounds of metal are often obtained 
in this manner from an apparently empty furnace. 

Every metallurgist should be capable of personally judging of 
the condition of his furnace bottom, as the shrewd smelter may 
gain great credit for speedy smelting by skimming his charges 
before they are really completed, while the honest furnace-man 
who waits until his hearth is clear before throwing the new charge 
may receive undeserved blame. 

The amount of detail connected with the management of a 
reverberatory smelting-furnace is almost endless, and while it 
may be an easier task to manage a reverberatory than a blast¬ 
furnace, for an inexperienced man, it is an infinitely greater attain¬ 
ment to be a thoroughly skillful reverberatory furnace-smelter 
than to have equal skill in the management of the blast-furnace. 

IMPROVEMENTS IN REVERBERATORY SMELTING. 

During the three years that have elapsed since the publication of 
the first edition of this book, there have been considerable advances 
made in reverberatory practice. Furnaces have been enlarged, 
improved methods for the removal of the slag have been adopted, 
and decided advances have been made in other directions. 

We are indebted to the Anaconda Works of Montana for some 
of these advances, but it is to Mr. Richard Pearce, of the Boston 
& Colorado Works at Argo, Colorado, that we owe the greatest 
gratitude in this direction. 

While there are several minor points of construction, and vari¬ 
ous points of practice that are not yet made entirely public, yet 
I can in the main describe these improved reverberatories, and 
the means by which their capacity has been increased from some 
16 tons to over 28 tons per day. 

In the first place, the size of the hearth of the furnace has been 
increased from about 10x15 feet to 14x24 feet. The hearth has 
also been materially enlarged by shaping it differently, and not 
drawing it gradually to a point at the flue-end as in the older 
practice, but keeping it nearly its full width until close to the 
flue, and then contracting it rapidly. 

The size of the fire-place has been increased by some 10 inches 
in length and 6 inches in width ; and although the amount of fuel 
used is of course larger than in the old furnaces, yet it has by no 
means increased in proportion to the additional capacity gained. 


REVERBERATORY FURNACES. 


325 


As the smelting-charges now amount to some (U- or 7 tons of 
ore, and the amount of slag is very great (especially in the Argo 
practice, where only about one ton of matte is produced to from 
12 to 18 tons of ore), it was found necessary to adopt some rapid 
and economical method of disposing of this great quantity of 
molten material. This is accomplished at Argo, as shown in the 
figures, by running it directly out of the furnace building in cast- 
iron spouts. 

To lessen the time required for skimming, this operation is 
executed from both the front door and the side door, opposite 
the tap-hole. The slag from each of these doors is skimmed into 
a conical pot, which answers as a settling-pot for the grains of 
metal, while the iron gutters lead from each of these pots to the 
front corner of the furnace on the same side as the side skim- 
ming-door. Here they unite in a third conical safety-pot, while 
from this pot another length of gutter carries the slag outside 
the shed, the length of it that crosses the working-space in front 
of the furnace being hinged at one end and counterweighted, so 
that it can easily be hoisted out of the way when not in use. 

To make this system perfect, this end-gutter should discharge 
direct into a large slag-car, or into a powerful stream of water 
that would granulate and remove the slag, the granules being 
subsequently removed into cars or to a high dump by means 
of an automatic bucket-elevator, but the conditions at Argo were 
not suited to such an arrangement, and the slag is simply run 
into sand-molds in the usual manner, and then loaded on railway 
cars, to be used as ballast for the line. 

All these arrangements are so simple and obvious, now that 
they are once in operation,,that they require little explanation. 

The gutters being very heavy, thick castings cool the slag so 
rapidly that it does not weld to them or damage them, and they 
consequently require no clay-fining, and last a long time. The 
matte also is tapped into iron molds, by which all adherence of 
sand is prevented, and less slag is made in the next operation, 
besides the great advantage of always having a clean shed, un¬ 
encumbered by a vast mass of heated and dusty sand. 

There is nothing new in preheating the air necessary for com¬ 
bustion before letting it pass under the grate-bars, but at Argo 
this preheating is more thoroughly and systematically executed 
than at any other works with which I am familiar. The cold ah* 



VIEW SHOWING POSITION OF FRONT AND SIDE SKIMMING DOORS, ALSO THE ARRANGEMENT OF SLAG SPOUTS. 



















LARGE REVERBERATORY FURJNACE. Side Elevation. 









































































































































































































































































































































































































































































































































































































































































































































































































































































































































































\ 



f 




LARGE REVERBERATORY FURNACE. Tap-Hole Side. Elevation. 














































































































































































































































































































































































































































































































































































































































































LAKGE REVERBERATORY FURNACE. Front Elevation. 






















































































































































































































































































































































































































































LARGE REVERBERATORY FURNACE. Rear Elevation. 


















































































































































































































































































































































































LARGE REVERBERATORY FURNACE. Longitudinal Section. 






































































































































































































































LARGE REVERBERATORY FURNACE. Sectional Plan. 


















































\ 



LARGE REVERBERATORY FURNACE. Cross Section. 























































- - - - 4’ "1 


W/, 


\t 




STACK OF LARGE REVERBERATORY FURNACE. Longitudinal Section. 




















































LARGE REVERBERATORY FURNACE. Skimming-Pots aud Slag Gutters. 













































VIEW OF FURNACE FROM TAP-HOLE SIDE, 













328 MODERN AMERICAN METHODS OF COPPER SMELTING. 


enters into channels formed in the brick-work near the front end 
of the furnace on each side, which openings are guarded by grat¬ 
ings. Thence it passes along deep side-walls, and close to the 
hearth-lining, and before it reaches the exit under the fire-box, it 
has become heated to a considerable degree. This system also 
assists in cooling the hearth-lining, and thus lengthening its life 
materially. Aside from this, heated air is allowed to enter 
through channels at either end of the bridge-wall, cooling the 
latter, and assisting greatly in the combustion of the gases, where 
it enters the furnace at the bridge. These openings are regulated 
by a valve, and to show that the benefit was not imaginary, my 
attention was directed to the difference in the flame shortly after 
throwing fire, and when these openings were alternately opened 
and shut. When closed, the flame was red and dusky, and a 
great volume of smoke escaped from the stack, while, on opening 
them, the flame at once became yellow and elongated, and the 
escape of smoke was almost entirely prevented. Others, includ¬ 
ing myself, have built furnaces with similar valve-openings to 
assist combustion, but owing to the ignorance and prejudice of 
the workmen, they have soon become blocked up and fallen into 
disuse. But Mr. Pearce has insisted on this point, until the 
smelters themselves have become convinced of their advantage, 
and now could not be persuaded to neglect them. 

A decided saving in time and fuel may be also effected in 
reverberatories that are running principally on calcined ore, by 
charging the red-hot ore from the calciners directly into the 
smelter, as is done at Anaconda, Montana. 

But this arrangement involves a plant laid out in a {peculiar 
manner, and in already established works it is often impracti¬ 
cable. 


But in building new works, where the ground and conditions 
are favorable, it should always be so arranged. The calciners, 
whether Bruckner’s cylinders or ordinary reverberatory-roasters, 
should be placed on a higher level than the smelting furnaces, so 
that the cars of hot ore from the former can easily be dumped 
into the iron hoppers of the latter. 

Bach calciner should be so arranged as to deliver its roasted 


ore into the hopper of each and every smelter, for, if using cylin¬ 
ders, the oidinary charge of 10 to 14 tons will have to be divided 
among three or four smelting furnaces j while, if hand-calciners 


REVERBERATORY FURNACES. 


329 


are used, it will require the combined charges of several of them 
to furnish enough ore for a single reverberatory charge. 

The use of red-hot, calcined ore by no means prevents the 
simultaneous addition of a greater or less proportion of cold ore 
from other sources, such as lieap-roasted ore, raw, dry ores, or 
even cold, calcined ores. But unless the hot calcined ore forms 
at least 50 per cent, of the total charge, it is hardly worth while 
to undertake this method of working, as there will not be sufficient 
time and fuel saved to make up for the delays and extra labor 
that it entails. 

This plan has been used so little and in so few places, that 
observations are mostly wanting as to the exact results obtained. 
From the statements of two gentlemen who are now using it to a 
greater or less extent, we may infer that where the charge con¬ 
sists mostly of red-hot, calcined concentrates, a saving in time of 
some 15 per cent., and in fuel of 20 percent, may be anticipated. 
But these statements are only given as guides, and are subject to 
correction. In a few months I hope to know more about this 
point, as I am at present planning a smelting plant where the 
main portion of the reverberatory charges will consist of red-hot 
concentrates from Bruckner’s cylinders, supplemented by a small 
addition of first-class lump ore, roasted in stalls. 

But though the utilization of the red-hot ore may not always 
be possible, there are certain improvements that are open to 
nearly every metallurgist, especially where he is called upon to 
plan new works, and is not hampered by old plants laid out on 
what is usually known in the profession as u The Patent English 
Wheelbarrow System.” 

Among these economies may be mentioned in particular: 

The charging of the furnace by means of a hopper, instead of 
the slow and extremely laborious practice of having the ore 
shoveled in through the side door. This plan not only saves the 
wages of at least one man to the furnace per shift, but also 
effects a far more important economy in time and fuel, for every 
manager must have frequently chafed over the long interval of 
time that elapses between the beginning of skimming and the 
final luting-up of the doors on a fresh charge. It is much less 
labor to spread the ore over the furnace-hearth as it falls from 
the hopper than would be imagined, and especially where red-hot 
ore is charged, as it flows in a sheet over the entire hearth almost 


330 MODERN AMERICAN METHODS OF COPPER SMELTING. 


as though it were a liquid. The presence in the furnace of the 
molten matte resulting from the last one or more charges is also 
of the greatest benefit in shortening the next period of fusion j as 
it not only keeps the fresh charge from sticking to the bottom, 
but it acts as a solvent in separating the particles of fresh ore 
and greatly hastening their fusion. 

It follows, therefore, that the matte should be tapped as seldom 
as possible, it being frequently advantageous to tap it only once 
in 24 hours 5 although this must depend upon the richness of the 
ore and the proportion of sulphur it still contains, as well as 
upon the depth of the hearth, and its capacity to hold a large 
quantity of matte. 


I 11 these large furnaces, taking 5 to 7 tons of ore at a charge, 
and especially if the ore is poor in copper, the amount of slag 
produced at each skimming is so enormous, that Mr. Pearce’s 
plan of having two skimming-doors—one at the side and the 
other in its regular position—greatly lessens the delay. 

The regular charging-door at the side of the furnace may be 
arranged for skimming, or a separate opening may be made close 


to it on the same side. 


The lining of a reverberatory stack is frequently burned out 
at short intervals, especially when the combustion of the gases 
does not take place perfectly in the hearth. 

Although the protection of this lining by an air-current is 
nothing novel, yet it is found profitable to go somewhat farther 
in this direction than the ordinary practice dictates. 

The chimney proper should be built some 15 inches larger 
inside than it is destined to be eventually • the inner fining being 
of 4J or 9 inches of fire-brick, solidly tied in at intervals with the 
red-brick casing, to make a strong wall. Inside of this, and sepa¬ 
rated from it by a 3-incli air-space, should come the false fining, 
consisting of one thickness, or 44 inches, of fire-brick. This forms a 
perfectly independent shaft within the main chimney, and only con¬ 
nected with the latter by an occasional cross brick for steadiness. 

By means of several ventilation holes through the casing of 
the stack below the flue, this air-space is placed in communica¬ 
tion with the external air, and a powerful current of cold air is 
established throughout its entire height, which more than doubles 
the fife of the false fining, and makes it exceedingly easy to 
renew it when worn out. 


REVERBERATORY FURNACES. 


331 


ESTIMATE OF MATERIAL AND LABOR ON NEW, LARGE REVERBERA¬ 
TORY FURNACES. 

Although the latest type of reverberatory furnace does not dif¬ 
fer from the old pattern, except in size, yet it may be useful to have 
at hand detailed estimates of the former, as well as full drawings, 
which accompany these estimates, and which may be relied upon 
as working drawings that may be used directly in construction* 

It will, of course, always be borne in mind, that different ores 
and different varieties of coal require differently proportioned 
furnaces; but under ordinary conditions, and with a fair quality 
of bituminous or lignite coal, the measurements here given will 
be found satisfactory. 

The amount that may be smelted in one of these large furnaces, 
depends entirely upon the particular conditions of each case. 
With favorable sulphide ores, calcined so that not too much of 
the iron is changed into a sesquioxide, and so that it may be 
charged red-hot direct into the furnace, and with the charging 
and skimming arrangements made practically automatic, as 
shown in the accompanying drawings, it is quite possible to smelt 
from 30 to 36 tons per 24 hours in this furnace. 

In a furnace of about the same size at the Argo Works, Mr. 
Pearce informed me that he had on an average put through 294 
tons of ore per 24 hours for an entire month. 

MATERIAL USED IN CONSTRUCTION OF REVERBERATORY. 

BRICK-WORK. 


Fire-Brick: 






Cubic feet. 

One 44" foundation-arch. 

22' 

X 

7' 

X 

44" 

58 

One 9" foundation-arch, inverted 

20' 

X 

15' 

X 

9" 

225 

One 44" flat hearth-bottom. 

20' 

X 

16' 

X 

44" 

120 

One 9" lining, both sides hearth 

46' 

X 

34' 

X 

9" 

121 

One front wall. 

10' 

X 

6' 

X 

9" 

45 

Two skewback walls of hearth .. 

46' 

X 

5' 

X 

9" 

173 

One bridge-wall. 

6' 

X 

6' 

X 

24' 

90 

One rear-wall, opposite skim-door 

8' 

X 

7' 

X 

134" 

63 

Two side-walls of fire-box. 

14' 

X 

9' 

X 

134" 

142 

Flue, doors, clamps, etc. 






123 

Lining of stack (see plan of stack) 






1,040 

Total. 






2,200 


* The drawings of the large reverberatory furnace that accompany this 
estimate were just completed for The Eastern Development Company, 
Limited, of Boston, and Cape Breton, N. S. And I am indebted to this 
company for the privilege of using them in this connection. 












332 MODERN AMERICAN METHODS OF COPPER SMELTING. 


2,200 cubic feet of fire-brick, at 18 brick per cubic 
foot, make, allowing for breakage and waste, 
40,000 brick, at $40 per thousand. 


Shaped Fire-Brick : No. 

Bull-heads. 250 

Side-skewbacks. 250 

End-skewbacks. 50 

Jamb-brick. 60 

Wedge-brick. 50 

Soaps. 50 

Splits. 100 


Total.. 810 


$1,600.00 


32.00 


Dinas brick for arch, 10,000 (used also in lining, etc.), at $60. 600.00 

Red brick for furnace and stack, 60,000, at $8. 480.00 

Fire-clay, raw and ground, 8 tons, at $8. 64.00 

Fire-clay, burnt and ground, 8 tons, at $8. 64.00 

Lime, 80 barrels, at $1. 80.00 

Cement, 80 barrels, at $1.50. 120.00 

Sand, 30 loads, at $1.50 . 45.00 


Total masons’ materials, 


$3,085.00 


IRON WORK. 


Cast-Iron: 






Pounds. 

One bridge-plate, ribbed and holed 

6' 

X 

3' 

X 

3i" 

2,500 

One rear bridge-plate. 

6' 

X 

26" 

X 

2" 

1,000 

Split plate for rear wall, ribbed .. 

GV 

X 

9" 

X 

H" 

600 

Plate to support rear of bridge. .. 

6£' 

X 

9" 

X 

H" 

600 

One front-plate, strongly ribbed.. 

6 / 

X 

2' 

X 

ir 

1,100 

One plate for end of fire-box. 

6*' 

X 

3' 

X 

i" 

950 

Two skimming-blocks, each. 

26" 

X 

6" 

X 

4" 

620 

Two door-frames. 






300 

Two skewback strips, in lengths . 

OO n 

X 

4" 

X 

1" 

2,200 

Three bearing and grating-bars.. 

6' 

X 

2" 

X 

3" 

432 

Gutters and pots. 






2,850 

Miscellaneous. 






1,200 

Total at 2\ cents per 

lb... 





14,352 I 


Wrought-Iron: 


Tie-rods of l$-inch round-iron : 

Feet. 

20 main furnace side-rods at 18^' 

370 

8 cross fire-box rods at 8 7 . 

64 

2 longest rods at 31P. 

63 

4 long main-hearth rods at 23^'. 

94 

Hooks, loops, etc. 

9Q9 

tUKJ ±J 

Total. 



Pounds. 


Carried forward. 


3,410 

3,410 $358.80 $3,085.00 


































REVERBERATORY FURNACES. 


333 


Brought forward. 3,410 $358,80 $3,085.00 

Iron for Stack: 

-8 uprights, f" x 1", 60' high, at 2£ lbs. per ft. 1,200 

100. cross-straps, 2" x x 8' long, at 13| lbs. each. 1,350 
Extra clamps for outside of stack . ' . 1,200 

Total at 2 cents per lb. 7,160 $143.20 

Buckstaves, old rails, say at 70 lbs. per yard: 


[These need only reach just below bottom of fire-brick hearth, 
though shown deeper in drawing.] 


Price, $25 per ton : 


Ft. 

20 for main part of furnace. 

. 6p high, 130 

4 for sides of fire-box. 

. 8' 

“ 32 

2 for end of fire-box. 

. 12' 

“ 24 

4 for upper shoulder. 

. 8' 

“ 32 

6 for front end. 

. 5' 

“ 30 

Bearing-bars, etc. 


50 

Total. 


.... 298 


Lbs. 


7,000 $87.50 


Total of iron-work. $589.50 

Miscellaneous : 

Lumber for patterns of arches, etc., 3,000 ft., at $18 .... $54.00 

Hoppers, complete. 140.00 

Excavation and stone-work. 300.00 

Grading and clearing up. 70.00 


Total. $564.00 

Labor : 

200 days masons’ labor at $4. $800.00 

220 u helpers’ “ $2 . 440.00 

10 “ carpenters’ labor at $3. 30.00 

10 u smith and helper at $5. 50.00 


Total. 

Incidentals and superintendence. 

RESUME OF TOTALS. 


Masons’materials. $3,085.00 

Iron-work. 589.50 

Miscellaneous. 564.00 

Labor. 1,320.00 

Incidentals and superintendence. 220.00 


$1,320.00 

$ 220.00 


Grand total. $5,778.50 

SMELTING FOR WHITE METAL. 

As the production of the higher grades of matte, of which 
white metal (from 70 to 75 per cent.) may he regarded as the type, 
by means of the fusion of calcined coarse metal with quartzose 



































334 MODERN AMERICAN METHODS OF COPPER SMELTING. 


ores, presents no sufficient differences from ore smelting to de¬ 
mand especial notice in this very brief treatment of the subject, 
the older process of concentrating metal without the intervening 
calcination need be alone considered under this head. 

This process is termed “roasting” by the English smelter, and 
denotes the gradual fusion of the coarse metal in large pigs, on 
the hearth of a reverberatory furnace, with the abundant admis- 
sion of air. 

It is seldom practiced in the United States on account of its 
extreme slowness and consequent great consumption of fuel and 
labor, but it possesses the advantage of great simplicity of plant, 
dispensing as it does with the entire crushing and calcining 
paraphernalia. 

Despite the simplicity of the process, much experience is re¬ 
quired to obtain the best results, as the exact degree of tempera- 
time at the differing stages of richness of the product has much 
to do with the rapidity of the concentration. 

Experience has taught that the rapidity of this concentration 
stands in exact proportion to the richness of the matte operated 
upon. The explanation of this is, that the sulphur, which is 
almost the sole foreign constituent of the richest matte, is very 
easy of oxidation, while the iron, which increases with the de- 
crease of copper, oxidizes with much greater difficulty. 

The writer has given much attention to this subject in connec¬ 
tion with futile efforts to effect what M. Manhes has now accom¬ 
plished with his Bessemerizing process. The following table 
gives, in per cent, of product, the result of his experiments, which 
extend over several years, many of them having been conducted 
for the Orford Copper and Sulphur Company, while.the author 
was in its employ. They were made merely to determine the 
rapidity with which the grade of the matte increases by the 
ordinary method, and without any attempt at Bessemerizing. 

Great care was taken in all instances to insure the correct 
sampling and assaying of the substances under consideration. 

It will be understood that the matte was charged in the shape 
of large pigs; melted down during the time indicated (in most 
instances, about five hours), and retained in a molten condition 
(in both stages with the free admission of air) for varying periods, 
samples being taken from time to time—after thorough stirring 
—to determine the progress of the concentration. 


REVERBERATORY FURNACES. 


335 


TABLE OF MATTE CONCENTRATION BY OXIDIZING FUSION — PERCENTAGES 

OF COPPER IN FRACTIONS OMITTED. 


Matte charged. 

When fully 

melted. 5hr8. 

6 hours. 

7 hours. 

8 hours. 

10 hours. 

12 hours. 

14 hours. 

16 hours. 

18 hours. 

20 hours. 

22 hours. 

24 hours. 

26 hours. 

28 hours. 

80 hours. 

32 hours. 

34 hours. 

36 hours. 

48 hours. 

16 

16 

17 

16 

19 

to 

© 

20 

21 

09 

21 



23 



23 



25 

29 

21 

23 

oo 




25 



27 



27 







33 

37 

41 


39 


41 



41 



44 



49 





41 

45 



47 


53 



54 



58 








50 

55 



57 


59 

. . . 


61 



61 



64 





58 

62 

62 

62 

61 

61 

62 


65 


65 


r- 

o7 

68 







63 

67 



70 


72 



75 



78 



84 





69 

73 

73 

74 

74 

77 

78 

77 

82 

85 



89 



94 


98 



74 

82 



84 


88 



94 




99 







80 

86 



89 


93 


98 












86 

94 






99 













92 

96 

96 

98 

99 




99 












96 

98 


99 




































THE MAKING OF BLISTER COPPER. 

This very beautiful and economical operation is entirely of 
English origin, and though virtually belonging under the head 
of “ Matte Concentration,” presents so many important peculiari¬ 
ties as to demand separate notice. 

The furnace used for this purpose, while an ordinary rever¬ 
beratory as regards size and shape, should be very strongly 
ironed, to withstand the large charges used in our modern prac¬ 
tice, while its bottom should be smelted in with peculiar care, 
and its upper layer should be thoroughly saturated, before used, 
with metal of the same grade as blister copper (from 96 to 98 per 
cent.), to prevent the certain annoyance from the rising of bits 
of the poorer matte just at the completion of the process, and the 
consequent adulteration of the whole charge of blister, which will 
require still further oxidation to remove the impurities. The 
lower bottom may be slightly saturated with lean matte to save 
expense. 

The metal is charged in large pigs, the total weight depending 
principally upon its grade; for as a full bed of blister copper 
(from 6 to 10 tons) is usually desired as most economical, it is 
evident that a much greater weight of blue metal (62 per cent.) 
will be required than of white metal (75 per cent.); while pimple 









































































































336 MODERN AMERICAN METHODS OF COPPER SMELTING. 


metal (83 per cent.) and regule (88 per cent.) will lose still less in 
the process.* 

The technical names just enumerated apply to various grades 
of matte, each of which has its invariable characteristics, which 
distinguish it with certainty. The percentages given there¬ 
with are not absolute, but are subject to considerable variation, 
the writer giving such average figures as his own experience has 
determined for him. 

As both economy and a due regard for the furnace bottom 
prevent the blister charges from covering too long periods of 
time, it is necessary to shorten the same by using either a less 
weight of matte, or insisting upon a higher grade at the outset. 

The latter is the proper choice, as a small charge is almost cer¬ 
tain to injure the furnace bottom by leaving a portion of it ex¬ 
posed to the direct heat of the flame. 

The most advantageous lengths for the working off of a blis¬ 
ter charge must depend largely upon local circumstances. From 
twenty-four to thirty-six hours will finish a full charge (eight 
tons) of rich pimple metal. 

A similar weight of white metal may require fifty hours, 
which is quite long enough for the safety of the furnace, though 
a much greater length of time often elapses without harm. “ 

As will be readily seen, it is impossible to work off a charge 
of blue metal within the prescribed limit of time, while even 
white metal extends the period most unpleasantly. It is there¬ 
fore much better with metal of low quality to divide the opera¬ 
tion into two stages—producing, for example, pimple metal or 
regule the first time, and bringing it up to blister copper by a 
second step. In this way, full charges can be used without en¬ 
dangering the furnace, and many advantages are gained. 

It is not well, however, to alternate the operations in the 
manner just suggested ; but rather to keep the furnace on one 


grade of metal until a large amount is collected, and then take 
up the blister process and maintain it until all the concentrated 
metal is disposed of. In this way, the evil of attempting to make 
blister copper on a bottom saturated with, poorer matte is 
avoided; and the exact amount of concentrated metal required 
for a full charge of blister can always be had. 


v Since this was written, blister charges have been fully doubled in 
w eight, the furnace hearth being made much larger than formerly thought 
practicable. 






REVERBERATORY FURNACES. 


337 


The matter may be pushed a step farther, by using a separate 
furnace for each operation, and positively interdicting the use of 
the blister furnace for any other purpose. 

The operation of making blister copper is frequently executed 
by constantly maintaining the charge in a molten condition after 
it is once melted, and never allowing it to chill or “ set,” as it is 
technically termed. 

By pursuing the latter plan, however, the danger to the hearth 
in long campaigns is greatly lessened, as it thus has a slight 
opportunity to cool, while the process is certainly advanced in a 
remarkable degree by the alternate fusions and cliillings. 

The belief that the operation of tapping causes a great gain 
in the grade of the matte, expressed among the Welsh smelters 
by the vulgar saying that “two tappings is worth one blowing,” 
is contradicted by the following experiment executed by the 
writer for the purpose of determining the truth or falsity of the 
common belief: 



Just before 


After 


tapping. 


tapping. 


Per cent. 


Per cent. 

No. 1 Copper. 

. 53-6 

No. 1 Copper. 

. 53-2 

No. 2 Copper. 

. 66-8 

No. 2 Copper. 

. 68-0 

No. 3 Copper. 

. 72-7 

No. 3 Copper. 

. 70-2 

No. 4 Copper. 

. 75-4 

No. 4 Copper. 

. 75 -2 

No. 5 Copper. 

. 79-3 

No. 5 Copper. 

. 79-1 

No. 6 Copper. 

. 85-4 

No. 6 Copper. 

. 86-2 

No. 7 Copper. 

. 94-0 

No. 7 Copper. 

. 93-2 

No. 8 Copper. 

. 98-7 

No. 8 Copper. 

. 98-5 

Average. 

. 625-9 

Average. 

. 623-6 


A few test assays that showed remarkable variation one way 
or the other were discarded, and, as seen, the others actually show, 
on an average, lower, rather than higher, grade of the metal after 
tapping, which is doubtless merely an accidental circumstance. 

The exact grade at which the blister copper should be tapped 
is a matter of much importance, as either too high or too low a 
copper presents physical qualities injurious to the requirements 
of the process. 

Blister copper of just the right grade is highly “ red-short ”; 
that is, can be easily broken when red-hot. It is this quality 
that enables the furnace-man to break and separate his pigs of 
blister copper, which operation is rendered greatly more difficult 
by a very slight variation in percentage in either direction. The 
proper condition of the charge is easily made manifest to the 
























338 MODERN AMERICAN METHODS OF COPPER SMELTING. 


experienced by ocular inspection, and the writer has endeavored 
to fix the limits that bound the grade of copper possessing this . 
important quality. 

Foreign impurities exert so much influence in this direction as 
to render impossible any exact establishment of such boundaries 5 
but numerous tests have fixed the most favorable grade between 
96^ and 99 per cent. 

An important precaution in the care of a blister furnace is 
the proper draining of the hearth and stopping of the tap-hole. 
Carelessness in this respect will permit a slight and unsuspected 
leakage during the entire period of blister-making, culminating in 
amass of metallic copper filling the entire tap-hole, and, as has oc¬ 
curred to the writer, requiring the combined efforts of the furnace 
personnel and blacksmith employes for twelve hours to remove it. 

The charge, being high blister, and just ready to tap, exerts a 
ruinous effect upon the furnace bottom during any such delay, 
and should be ladled out at once under similar circumstances. 

The slag from the blister process, being very rich in oxide of 
copper, should be returned to some process where the product is 
of high grade, and not, as is often the case in this country, sent 
back to the ore smelting, where its copper contents are thrown 
back again to the condition of a base sulphide. 

The following are examples of the composition of the slag 
and copper produced by this roasting-smelting for blister copper, 
taken from Mr. Howe’s paper already referred to : 



U 

O 

OQ 

0 * 

- 

- £ 

& 12 

£ 

“ Roaster ” slags 
from Kaaflord.t 


Welsh blistered 
copper. 

Blistered copper, 
from Kaaflord.t 

Silica. 

47-5 

36-0 

Copper. 


99•2-99■4 

Protoxide of iron. 

28-0 

7-0 

Iron. 

• 7-0•8 

0-1- 0'2 

Alumina. 

3-0 

6-0 

Nickel and cobalt.. 

0•3-0•9 

0-2- 0-3 

Cuprus oxide, Cu 0 0. 

16-9 

43-2 

Zinc. 


0-0- 0-02 

Lime. 


2-7 

Tin. 

0•0-0•7 

Magnesia. 


0-8 

Arsenic. 

0•4-1•8 


Nickel and cobalt oxides. 

0-9 

4-9 

Sulphur. 

0’1-6•9 

0-1- 0-12 

Oxide of tin. 

0-3 

0-6 




Oxide of zinc. 

2-0 

3-2 





*Le Play. Op. cit., p. 218. 

tKerl, Grundriss der Metallhuttenkunde i., p. 215. 











































REVERBERATORY FURNACES. 


339 


THE USE OF BASIC-LINED FURNACES. 

Various attempts have been made at different times to con¬ 
struct the hearth and lining of blister-furnaces of some material 
that would have a purifying effect upon the copper treated 
therein, by absorbing deleterious constituents, and thus hastening 
the purifying process. 

But none of these efforts have been sufficientlv successful to 

e/ 

gain any firm hold upon the profession, and my own experience 
in this direction has plainly shown me their futility. 

Within the past two years, however, Percy C. Gilchrist, A. R. 
S. M., has made an elaborate series of experiments of a somewhat 
novel character, and that according to his own statements, as 
well as in the belief of many metallurgists who are qualified to 
judge of the matter, have led to a positive improvement and 
economy in that branch of copper-metallurgy known as the 
“ Blister Process,” as well, though in a considerably less degree, 
as in the actual refining of the blister copper. 

Mr. Gilchrist published a full account of his discoveries in The 
Journal of the Society of Chemical Industry, published in Eng¬ 
land, in January, 1891, and while I intend this work to be mainly 
a record of my own experience, I feel it necessary to briefly point 
out the very remarkable results obtained by Mr. Gilchrist, and 
which I hope before long to be able to speak of from personal 
trial. 

The most common serious impurity in copper is arsenic. 
This is especially the case in England, where our pure ores are 
the exception rather than the rule, and where the copper smelters 
are expected to make good copper from material carrying one, 
two, and even five per cent, of arsenic. 

At the works where Mr. Gilchrist made his experiments, a 
large amount of highly arsenical copper-precipitate is treated, 
being added in varying amount to the slag and matte charged 
in the second smelting operation. 

The mixture is so regulated that there is not sulphur enough 
present to combine with all the copper. Therefore, the product 
of a quick fusion of the above mixture consists of a considerable 
quantity of rich matte, comparatively free from arsenic, and a 
much smaller quantity of very impure metallic copper, known as 
u Metallic Bottoms.” 


340 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Arsenic has a much greater affinity for metallic copper than 
it has for matte; hence by this simple operation, the main por¬ 
tion of the arsenic is concentrated into a small quantity of very 
impure “ bottoms,” while the great bulk of the copper is obtained 
in the shape of a matte of reasonable purity. 

If gold were present, it would also concentrate very perfectly 
in the “ bottoms,” as is well known to all copper smelters, who 
use this method extensively in treating auriferous mattes. 

An average analysis of these “ bottoms ” gives: 


Copper. 
Arsenic 
Sulphur 
Iron. .. 
Lead... 
Silica.. 


Per cent. 
83 to 87 

5 “ 7 

1 “ 3 

0-5 
3 “ 5 

0*5 


It is in the conversion of these very impure u metallic bottoms ” 
into blister copper containing under one per cent, of arsenic that 
Mr. Gilchrist’s treatment seems to most plainly show its value. 

Having been much annoyed, as are all copper refiners, by the 
enormous amount of rich slag resulting from the long, slow melt¬ 
ing and refining of these bottoms into blister copper; and knowing 
this slag to be in the main a silicate of copper, the silica of which 
must come from the hearth and lining of the furnace, it occurred 
to him that if he should use a basic hearth and lining, the amount 
of slag should be greatly decreased, owing to the absence of any 
silica to combine with the oxide of copper. 

Obtaining permission from the Company to make the experi¬ 
ment, he proceeded at once to put in a hearth of the same basic 
material as is used in steel furnaces; mixing the ground material 
with tar in the usual way, and burning it onto the bottom of the 
furnace in layers; each layer being well beaten down and fired 
for some hours, before applying a fresh one. This is a some¬ 
what tedious operation, requiring some 4 or 5 days to properly 
burn in a basic bottom. 

The taphole of the furnace is closed by throwing a little basic 
material against its internal opening, and the basic hearth absorbs 
in time just about the same quantity of copper as the ordinary 
quartz hearth. 

Like the latter, it must be carefully u seasoned” by smelting 








341 


REVERBERATORY FURNACES. 


a few light, quick charges of rich copper precipitate, or good 
blister copper upon it, tiU it lias absorbed sufficient copper to 
make it solid and hard. 

The repairs to the fettling of this furnace are very slight, as 
the tendency is rather for the fettling to grow than to cut away. 

The practical merits of this new departure are emphatically 
shown by the fact that in a few months after the first basic 
furnace, the Company had nine of its blister furnaces fined in 
this manner, and intended to alter all the others as fast as they 
wore out. 

The following table from Mr. Gilchrist’s paper shows in a 
condensed form the extraordinary and favorable difference pro¬ 
duced by the use of a basic fining. I will remind my readers, 
that in English metallurgical nomenclature, blister furnaces are 
called “ roasters,” and the operation of blister making is known 
as “roasting”. 


COMPARATIVE STATEMENT OF METALLIC BOTTOMS, ROASTED, RESPECTIVELY, 

IN BASIC- AND SAND-LINED FURNACES. 


Metallic bottoms charged during 12 weeks : 
Average analysis, 84’52% copper, 5*91% arsenic. 

59 charges made, averaging about. 

Blister copper produced from same. 

Average produce per charge, averaging 1*11% As 

Slag made from above charges. 

Average weight of slag per charge. 

Average per cent, of copper in slag. 

Time occupied per charge, including fettling, etc, 


Ba?ic Sand 

Furnaces. Furnaces. 

Tons of 2,000 lbs. 
448.56 448*56 

7*574 7*574 

362*124 214.76 

6*132 3*64 

115*178 248*36 

1*946 4*2 

25fo 55% 

29£ brs. 38 hrs. 


A careful study of the above table will be found very instruct 
ive. In the first place, assuming the “metallic bottoms” that 
were charged into the furnaces to average 84 - 52 per cent, copper, 
and the blister produced to average 98b per cent, copper; it will 
be seen that from the furnaces with basic fining, the remarkable 
yield of 94 per cent, of the copper charged was obtained in the 
shape of blister copperj while from the ordinary furnaces, only 
56 per cent, was obtained, a gain of 38 per cent, in favor of the 
basic furnaces. 

This simply means, that by the use of the basic fining, the 
amount of slag to be re-treated from the blister process is reduced 
more than 50 per cent., there being only 115 tons of slag instead 










342 MODERN AMERICAN METHODS OF COPPER SMELTING. 

of 248, as produced in the acid furnaces. And when we come 
to estimate the amount of copper tied up in this slag, the advan¬ 
tage of the basic lining becomes still more apparent 5 for not 
only does it produce less than one-lialf the total quantity of slag, 
but this slag carries less than half the percentage of copper 
that the slag does that is produced in ordinary furnaces j being- 
only 25 instead of 55 per cent. The actual amount of copper in 
the basic furnace slag is only 28f tons instead of over 13G 
tons as in the acid-lined furnace. Thus, only about one-fiftli as 
much copper goes into the slag where the basic fining is used • 
which means that four-fifths of the copper that goes into the slag 
during the common blister operation is hereby saved, and goes 
at once to market without any further expense than has to be 
put on all the blister copper. 

But this by no means represents all the advantage that arises 
from the employment of a basic hearth. It is a well-known fact 
to all copper-refiners that the production and treatment of these ar¬ 
senical “ metallic bottoms / 7 and the long period that this immense 
mass of molten copper has to be kept in the furnace to permit 
the arsenic to become gradually volatilized, have a most destruc¬ 
tive effect upon the hearth of the furnace, which usually requires 
quite extensive repairs after every few charges, and frequent, 
radical renewals. 

This heavy expense has stopped the production of “ metallic 
bottoms 77 at most of the British smelters, the managers finding it 
more profitable to charge their copper-precipitate into the smelt¬ 
ing furnaces, together with sulphide ores, and thus “ throw it 
back 77 into a matte. 

But by the use of the basic hearth, this expensive repair bill 
is almost entirely suppressed, and the full advantages arising 
from the formation of “ metallic bottoms 77 are obtained without 
the heavy costs commonly connected therewith. 

TREATMENT OF WHITE OR PIMPLE METAL ON THE BASIC HEARTH. 

Although such striking advantages are not obtained in smelt¬ 
ing matte in a basic furnace as in the treatment of “ metallic bot¬ 
toms,” yet a very considerable gain in output results therefrom. 

Mr. Gilchrist gives the result of a long series of comparative 
trials by which it was ascertained that there was a gain of from 
20 to 30 per cent, in the amount of copper produced in favor of 


REVERBERATORY FURNACES. 


343 


the basic furnace. This means, of course, a very large saving in 
the subsequent treatment of the blister slag. 

Arsenical copper frequently arrives at blister pitch, but still 
contains too much arsenic to tap, and has to remain molten 
under an oxidizing flame until the arsenic is reduced to the 
desired limits, usually under one per cent. 


It is found that the use of the basic furnace favors the 
removal of the arsenic, and greatly shortens the period of oxida¬ 
tion, the relative time, in hours, being found on an average to be 
about 6 for the basic, and 10 for the ordinary, furnace, or a sav¬ 
ing of some 40 per cent, of time in favor of the new method. 

The use of the basic hearth in refining copper was also care- 
fully investigated by Mr. Gilchrist, and his results and deduc¬ 
tions will be found at the close of the chapter on copper refining. 


COPPER REFINING. 

The only method of copper refining practiced in the United 
States, or, in fact, in the civilized world, is the ordinary Swan¬ 
sea process.* 

The purity of our local ores and the simplicity of our trade 
requirements have prevented the development of those marked 
variations that characterize the English process, where “best 
selected,” “ tough cake/’ “ founder’s metal,” and many other dis¬ 
tinct varieties are demanded and produced. 

The great excellency of the Lake Superior copper, derived 
from pure metallic ores, has established a very high standard in 
our markets, and owing to the abundant supply of the same, 
manufacturers have not, until recently, found it necessary to 
study the behavior or familiarize themselves with the capabilities 
of other brands of copper for certain uses, but, feeling sure that 
if they bought the best they would be safe, have employed this 
unnecessarily superior metal for the manufacture of brass cast¬ 
ings, and many other purposes where a poorer quality would 
have served equally well. 

The most impure domestic coppers are often sufficiently 
argentiferous to repay a separate process by which the quality 
of the baser metal is improved, while the nobler is saved—of 
late largely by electrolytic means. 


* A few unimportant exceptions to this statement may still exist. 



344 MODERN AMERICAN METHODS OF COPPER SMELTING. 


The refining-furnace presents no peculiarities to distinguish 
it from the ordinary English reverberatory, except that it should 
be more strongly constructed j being provided with a massive 
front plate—below the skimming-door—as well as strong hori¬ 
zontal, lateral braces to strengthen the hearth, which, in addi¬ 
tion to the enormous expansive force caused by the high tem¬ 
perature, must also sustain the weight of from 10 to 15 tons of 
molten metal. 

The ash-pit is very advantageously provided with iron doors, 
which may be closed during the ladling, to exclude all currents 
of air, while the flpe is brought as nearly as possible oyer the 
skimming-door, in order that the air-current that enters there¬ 
from may ascend at once without affecting the metallic bath. 

The two bottoms are smelted in with unusual care, and the 
upper one thoroughly saturated with repeated small charges of 
metallic copper. This should be spread over the entire surface 
in the shape of granules, and should be rapidly fused until it is 
entirely liquid. At first, nearly all will be absorbed, but event¬ 
ually, a larger and larger proportion will be regained, and 
thoroughly dipped from the ladling-hole at the close of each 
operation. A hearth of the ordinary size, 94 feet by 14 feet, will 
absorb from 6,000 to 18,000 pounds of copper during the “ soak¬ 
ing ” process, according to the quality of the sand and the tem¬ 
perature attained during the “ smelting in ” of the bottom. 

On no account should metal of poor quality be used for pur¬ 
poses of saturation. This is a fatal economy, as the grade of all 
copper refined in the furnace for many months may be affected 
thereby. 

Even after the bottom is well saturated and has attained a 
considerable degree of firmness, the careful refiner will avoid 
any possible injury thereto from heavy masses of metal. It is 
not uncommon to charge pigs of blister copper weighing 1,000 
pounds or more, the sharp corners and edges of which are very 
likely to cause indentations and unevenness in the toughest bot¬ 
tom, which may serve as the starting-point for serious after¬ 
effects. All such injuries may be avoided by laying down a 
rough floor of old planks or similar material. 

The fuel best suited to refining is a not too caking bitumi¬ 
nous coal with long flame. Sulphur-bearing coals should be 
avoided, as tending to alter the “ pitch ” of the metal at critical 


REVERBERATORY FURNACES. 


345 


moments. Where such coal is expensive, a cheaper variety may 
be used for the earlier stages of the process. 

No better fuel exists for refining than wood, as its freedom 
from sulphur and other impurities, and the long, pure, non¬ 
reducing flame that it yields, peculiarly fit it for the purpose. It 
was used entirely at the Ore Knob Refining-Works with great 
satisfaction, and would be more frequently employed were it 
cheaper at the great copper centers. 

The capacity of a refining-furnace should be increased by 
deepening the hearth rather than enlarging its area, as the diffi¬ 
culty of retaining the copper in proper pitch is greatly height¬ 
ened by increasing the surface area. Within certain limits, this 
may be effected by constructing a clay dam at the skimming- 
door; beyond this, the deepening must be effected by lowering 
the bottom, which, in any case, must pitch toward the ladle-liole 
from every point. 

The size of the charge is limited rather by custom and the 
capacity of the attendants than by the size of the furnace, and 
has been greatly increased of late years. 

During the writer’s student years a charge of 14,000 pounds 
was considered large, but the present English refiners vary from 
18,000 to 25,000 pounds and upwards. 

The Lake Superior refineries are charged with some 18,000 
pounds at 80 per cent. “ mineral,” producing over 14,000 pounds 
of pure copper. Of late years this charge has been increased 50 
per cent, or more. This may be regarded as an average quan¬ 
tity ; but the Orford Company, ever foremost in increase of 
capacity, has found no difficulty in refining charges of even 
30,000 pounds. The principal trouble with large charges is the 
tendency of the refined copper to get u out of pitch,” when 
retained in a molten condition for so long a time that fresh coal 
must be several times thrown upon the grate. Another difficulty 
is the want of room between hearth and roof to accommodate 
such a weight of metal. The shape and irregularity of the pigs 
of blister copper, and the difficulty of accurately placing such 
awkward bodies in the desired position in a red-hot furnace, have 
also prevented the ordinary use of larger charges. This is 
remedied in the Lake furnaces by lessening the customary pitch 
of the roof from bridge to charging-door, and curving it down 
abruptly at the latter point. 



REFINING-FURNACE AT THE LAKE SUPERIOR REFINING-WORKS.—SIDE ELEVATION. 





































































































































































































































































































































































REVERBERATORY FURNACES. 


347 


Great care must be observed regarding the quality of all 
material allowed to enter the refining-furnace. It is not an 
apparatus for the concentration of matte, but simply to alter the 
shape of metal that is already nearly pure, and to put the finish¬ 
ing touches on it. Much of the pig-copper produced from blast¬ 
furnace work from both carbonate and sulphide ores may advan¬ 
tageously undergo a preliminary purifying process in the blister 
furnace. All copper below 96 per cent, should be thus treated ; 
a mere melting down with free admission of air being sufficient 
to produce a 99 per cent, blister copper in most cases, so that two 
charges of 16,000 pounds each can be thus treated in twenty-four 
hours. 

A few hundred pounds of the richest refinery slag from the 
last skimming may be returned to the same operation, the rest 
going back to the last preceding operation. 

Cement copper from wet processes should, in most cases, be 
treated in the blister furnace. It must be thoroughly dampened 
to prevent mechanical loss, and when mixed with white metal to 
the extent of one-fourth or one-third of the entire charge, assists 
so materially in enriching the product and in shortening the 
operation that it just about repays the cost of its treatment. 

Mr. James Douglas, Jr., has regularly produced so pure cement 
copper, by both the old and new Hunt & Douglas process, that 
it is refined at once with advantage. The principal drawback is 
its excessive bulk, which renders it necessary to add the cement 
copper in several successive portions, to obtain a full charge. 
This may be obviated by pressing it into bricks while yet damp. 

Only one charge can be treated in a refining-furnace each 
twenty-four hours, and in ordinary cases, the labor connected 
therewith consists of one head refiner, three or four ladlers 
(according to whether the refiner acts also as ladler), one night 
refiner, one man to lift the ingots from the boshes, one to dump 
the molds, and one to remove any accidental impurities from the 
ladles, dry the molds, etc. The latter three operations are often 
conducted by boys. One man is also required to remove the 
ingots to the packing-house, while the packing itself, and the 
transportation and manipulation of the new charge, are effected 
J>y the furnace personnel , which usually expects to conclude the 
dav’s labor by three p.m. The work is very hot and severe while 
it lasts, and in the cases of the large charges referred to, extra 



REFINING-FURNACE AT THE LAKE SUPERIOR REFINING-WORKS.—LONGITUDINAL SECTION, 





















































































REVERBERATORY FURNACES. 


349 


assistance may be required for packing the copper and similar 
extraneous work. 

While the quality of the copper depends largely upon the skill 
of the refiner, its external appearance and neatness are princi¬ 
pally influenced by the ladlers. As these latter qualities exercise 
an undue influence upon the sale of copper in this country, it is 
of great importance to create a body of trained and skillful 
workmen, whose pride, as well as self-interest, is enlisted in the 
matter. 

The color of the copper has an influence with American 
buyers entirely disproportionate to its importance as a sign of 
purity. A deep rose-red is the color most prized, while any 
brassy appearance is very damaging in the eye of the buyer. 

As this dirty yellow appearance can be produced at pleasure 
by allowing the copper to remain a few seconds too long in the 
molds before it is dumped into water, while the poorest copper 
may be colored a fine, deep red by lifting it out of the water for 
a second immediately after dumping, and then returning it again 
to the trough, as well as by the use of any one of innumerable 
baths or u pickles,” it certainly should not be regarded as of such 
vital importance. It is true, nevertheless, that pure coppers take 
on the desired color with much greater ease than those containing 
arsenic, antimony, or various other substances, and in the case 
of the remarkably pure Lake Superior metal, it is even difficult 
to produce that dreaded brassy appearance which any impurity 
of water or want of care is certain to develop in ordinary cases. 

The red color is produced by the formation of a minute film 
of suboxide of copper; but why this hue should be affected by 
slightly brackish water, or by changes of temperature in the 
cooling water, it is difficult to understand. Pure water should 
be used and the most favorable temperature discovered for each 
variety of copper. In some cases, it must be nearly boiling • in 
others, ice-cold; while in still other instances, the refiner cor¬ 
rects an unfavorable coloring by the introduction into the cool¬ 
ing-boshes of soda-ash, salt, sawdust, coal ashes, and various 
other apparently inactive substances. 

The refining-furnace usually receives its fresh charge immedi¬ 
ately after it has been emptied of the preceding one. The fire is 
not urged until evening, in order that the first two stages of the 
operation, the fusion and the refining, may not be completed before 


Pig. 3 



REFINING-FURNACE AT THE LAKE SUPERIOR REFINING-WORKS.—PLAN SECTION. 






















































































































a Fire place. 

6 Ash-pit. 
e Bridge wall. 

d Air passage controlled by valre e. 

e Bridge valve. 

f Air passage controlled by the valre g. 
g Roof valve. 

h Laboratory of the furnace. 
i Hearth of sand & copper. 

J Arch supporting the hearth. 
k Charging door. 


Working door. 
m Fire door, 
n Chimney 58 feet high, 
o Flue to n. 
q Movable roof. 

s Cast Iron T bars holding furnace together. 

t Air passages leading to d. 
u Socket for bars v and ix 
v Bar for the repair spadeL 
w Pole bar. 
x Bar of movable roof. 


REFINING-FURNACE AT THE LAKE SUPERIOR REFINING-WORKS. REAR 

ELEVATION.—SCALE,, i" = 1'. 























































































































































































































































































352 MODERN AMERICAN METHODS OF COPPER SMELTING. 


the day shift conies on to execute the refining proper-—the third 
and final stage. 

With pig-copper of reasonably good quality, the process of 
fusion may be begun at seven or eight P.M., and be pushed as 
rapidly as possible. Owing to the high heat-conducting quality 
of this metal, the pigs retain their shape until the fusing-point is 
reached, when they soften and melt almost instantaneously. 
From the reducing character of the flame, only slight chemical 
changes have thus far been produced j but as soon as the pro 
tecting layer of slag is removed from the surface of the bath, 
and air freely admitted, the process of purification proceeds with 
great rapidity, from the direct oxidation of the foreign sub¬ 
stances present, as well as the more far-reaching and power¬ 
ful reaction of oxide of copper upon all those metalloids and 
bases that have a greater affinity for oxygen than the copper 
itself. A thin slag forms rapidly upon the surface, and is re¬ 
moved at intervals of an hour or so. The constant escape of 
anhydrous sulphuric acid causes a persistent ebullition, which 
tends greatly to facilitate the process of oxidation. As the pro¬ 
portion of base metals becomes diminished, the slag is more 
strongly colored with the red oxide of copper, until that pro¬ 
duced toward the close of this stage contains from 40 to 70 per 
cent, of this metal, and becomes a valuable oxidizing flux for the 
preceding blister process. The total amount of slag produced 
during the operation of refining depends principally upon the 
quality of the pig-copper, but is seldom less than 12 per cent, of 
the entire charge, containing from 4 to G per cent, of the total 
weight of copper. 

The gradual cessation of ebullition and the rapid formation 
of oxide of copper by no means indicate the entire disappearance 
of the sulphur present, which, from its strong affinity to copper, 
remains dissolved in the bath with great tenacity. If the oxi¬ 
dizing process has been sufficiently thorough to insure the pres¬ 
ence in the liquid metal of a perceptible quantity of suboxide of 
copper (from 0*2 to 0*7 per cent, according to different authori¬ 
ties), a small sample ingot poured at this stage will exhibit a. 
very peculiar and characteristic phenomenon. On cooling, it will 
suddenly rise in a line along the center, often forming an abrupt 
ridge several lines in height, and having an irregular and granu¬ 
lar fracture. This is said to be due to the absorption of sulphur- 


























































354 MODERN AMERICAN METHODS OF COPPER SMELTING. 


ous acid, a property only possessed by metal containing a consid¬ 
erable proportion of snboxide of copper, but still unrefined and 
tenaciously holding on to a trace of sulphur and other impurities. 
The process of “flapping” or “rabbling” is now begun, by which 
the liquid bath, through the side door, is constantly agitated in a 
peculiar manner by means of a small rabble. 

It is, of course, a purely oxidizing operation, both tedious 
and slow, requiring, on an average, two hours of constant 
work. Although seemingly a most awkward and ineffectual 
means of agitating an extensive bath of molten metal, and bring¬ 
ing all its particles in contact with the atmospheric air, it lias 
never.been improved upon. The copper now becomes “dry” 
from the dissolved suboxide, and when poured into a mold, sets 
with a deep depression upon its surface, while its fracture has a 
characteristic mottled appearance, following upon a previous 
fine-grained surface, as particularly mentioned by Professor 
Egleston in his valuable paper on Copper Refining in the 
United States. The color is a brick-red, but both grain and 
color are so influenced by the temperature at which the metal is 
poured, as well as by the rate of cooling as determined by the 
size of the test-ingot, that these signs must always lie taken in 
conjunction with other and more reliable indications. The metal 
during this period is undergoing a powerful scorifieation from 
the dissolved oxide of copper, and most injurious impurities are 
gradually oxidized, and either effectually removed by slagging 
or volatilization. Certain metalloids, however, resist this scori¬ 
fying influence to a remarkable degree, and consequently have a 
most injurious effect upon the refined metal. These are arsenic, 
antimony, and tellurium, mentioned in the order of their fre¬ 
quency. The extreme importance of the subject warrants the 
mentioning of the best means to remove the two first-mentioned 
impurities, the latter having come but once within the author’s 
experience, and probably requiring the employment of one of the 
electric or chemical methods, by which excellent copper can be 
made from very poor material. 

A careful trial of Vivian’s invention of dry-sweating, by 
which the impure blister copper is exposed to a long oxidizing 
heating just below the fusion-point, has not succeeded with the 
writer; 1 )ut the addition of from 3 to 5 per cent, of pure white 
metal—subsulphide of copper—to the bath at the beginning of 




SECTIONAL PLAN. 










































































































































































356 MODERN AMERICAN METHODS OF COPPER SMELTING. 


tlie refining process (as suggested by some person forgotten by 
the author) lias a most rapid and satisfactory effect in removing 
both arsenic and antimony. Very bad cases may require two 
.such additions, with an intervening oxidizing operation. A still 
more sure and radical method consists in exposing the arsenical 
ore to a dead roast, and subsequently smelting the same with a 
large proportion of iron pyrites—cupriferous, if possible. The 
resulting low-grade matte should be regarded and treated as a 
sulphide ore, and will, if the initial calcination is thoroughly 
conducted, be free from either arsenic or antimony.* 

The process of reduction follows that of oxidation, and the 
suboxide of copper, having served its purpose as a purifying 
agent, must now be reduced to metal again ; otherwise) the cop¬ 
per would be brittle both when cold or at higher temperatures, 
and unfit for manufacturing purposes. The reduction is effected 
by means of a long pole, as large as can be introduced into the 
furnace and of any kind of green wood—hard wood being the 
most economical. This, being buried in the metal bath, evolves 
an immense volume of hydrocarbons and other reducing gases, 
and rapidly removes the excess of oxygen. The surface of the 
metal is also covered with charcoal, to prevent access of ah*, and 
samples are constantly taken to determine the condition of the 
copper. The entire removal of all the oxygen present is impos¬ 
sible, even over-poled copper, according to Egleston,f containing 
over O'l per cent, of oxygen. And otherwise tough copper may 
become brittle from over-poling, and this is doubtless due to the 
fact that the impurities that were present in the tough copper 
were dissolved as oxides and consequently innocuous, but on 
being reduced to the metallic state, at once asserted then* delete¬ 
rious influence. 

The poling usually lasts an hour or more, and is continued 
until a full-sized test ingot shows no contraction or depression 
on cooling, and the texture is extremely fibrous and silky, and of 
a beautiful rose-red. Further tests are made by nicking and 


* The author is unable to give the original sources of many statements 
here made and tested by himself with satisfaction, and desires to distinctly 
disclaim any originality in any operation or apparatus pertaining to copper 
metallurgy; having always preferred to adopt those improvements that 
have been thoroughly tested by others of a more original turn of mind, 
t See Copper Refining at Lake Superior , by T. Egleston. 




SECTION E.'F. 


Fig.4 



FIG. 4. 


FRONT ELEVATION, 








































































































































Fig. 5 



PITTSBURG COPPER-REPINING FURNACE.—ST AM P FOR INGOT MOLD. 

















































































REVERBERATORY FURNACES. 


359 


bending test bars, and by hammering out a piece into a thin 
plate, which should show no cracks at the edge. This condition 


of tough-pitch is essential to copper used for rolhng or wire 
drawing, but is entirely superfluous for ingot copper that is to be 
used for brass founding, as it may be easily imagined that the 
fusion that it undergoes in the brass-founder’s crucible, under 
various oxidizing and reducing influences, effectually upsets the 
exquisite niceties of the refining process, so far as the proportion 
of dissolved suboxide is concerned. 


A volume could be easily filled with practical comments upon 
the process of refining, but space forbids any further details. 
The addition of lead to copper intended for rolling is quite com¬ 
mon in England, and is doubtless beneficial to many impure 
coppers. The purer copper of the Lake district and from the 
Arizona carbonates does not seem to receive any benefit from this 
practice. 

The molds used for the casting of ingots should always be 
made of copper, and are easily and rapidly produced by the 
ordinary ingot stamp, as illustrated herewith. The proper taper 
of the mold and the proportion of surface in contact with the 
ingot have an important effect upon the ease with which the 
mold delivers. When the copper is ladled too hot, the molds are 
rapidly ruined, and as at best they wear rapidly, they should be 
returned to the refining furnace as fast as they become in the least 
imperfect; otherwise, constant annoyance and accidents will re¬ 
sult from the obstinate sticking of the ingots. 

The ladles used in the refining process come almost exclu¬ 
sively from England, and are made of a peculiar quality of iron. 
They last from 10 to 100 operations, according to the tempera¬ 
ture of the copper and the care bestowed upon them. 

The Ansonia Brass and Copper Company has patented a new 
mold for casting ingots directly from the furnace, without the 
intervening process of ladling. While such an improvement 
woidd relieve the workmen from the hot test and most laborious 
portion of the operation, the very nature of the metal, its high 
fusion-point and great heat-conducting capacity cause it to chill 
so suddenly as to render the success of such an invention a mat¬ 
ter of some doubt. The same company employs a gas generator 
for heating a single refining-furnace, and although pronounced 
convenient and successful, it can hardly make any great saving, 


360 MODERN AMERICAN METHODS OF COPPER SMELTING. 





DETAILS OF INGOT. INGOT MOLD, SHOE AND TANK. 













































































































REVERBERATORY FURNACES. 


361 


considering the small amount of fuel generally used in ordinary 
refining, and the great expense of the generator plant. 

A great saving in the expense of refining has already been 
made by increasing the capacity of the ordinary furnace, and the 
next important improvement may be looked for in bettering 
the quality of the refined copper and increasing its strength and 


tenacity. How this is to be effected is far too difficult a sub¬ 
ject to be discussed within the limits of a practical paper on 
existing methods. Experiments conducted by Mr. Patch, of the 
Detroit Copper Company, as well as the writer’s personal trials, 
seem to indicate that the presence of suboxide of copper is by no 
means essential to the greatest malleability and strength, as 
believed by Percy, and that a proper method of treatment may 
result in the production of copper having a strength far beyond 
the best brands at present known. 

The cost of refining varies so greatly with the purity of the 
blister copper treated, and depends also so completely upon the 
size of the charge, that no absolute estimate of expense can lie 
given. 

The following figures, taken from actual practice, give a fail* 
idea of the cost of refining ordinary Arizona pig-copper of from 
95 to 98 per cent.—being about equivalent to good Chili bars. 
The size of the charge is assumed to be sufficient to produce 
24,000 pounds of refined metal, the furnace running regularly, 
and making one charge every twenty-four hours, while the ex¬ 
pense of foremen, etc., is supposed to be divided between two 
furnaces. 

Cost of refining one charge, yielding 24,000 pounds of cop¬ 
per— 


Coal—best quality—3'8 tons, at $5.50. 

Clay and sand for fettling—450 pounds. 

Cheap clay and loam for doors and slag-beds—400 pounds 

Poles—45 feet of 6-inch poles, at 4 cts. 

Charcoal—6 bushels, at 10 cts. 

Proportion of cost of renewing bottom. 

“ “ “ main arch. 

11 “ u flue. 

11 “ other repairs on furnace. 

For renewing tools, barrows, ladles, etc. 

Repairs on ditto. 


$20.90 

.95 

.30 

1.80 

.60 

.34 

.62 

.32 

.72 

1.11 

.64 


Carried forward 


$28.30 














362 MODERN AMERICAN METHODS OF COPPER SMELTING. 


Brought forward ..$28.30 

Lights, oil, soap, clay-wash, brushes, etc.70 

Cost of resmelting poorer slag in blister furnace. 1.20 

One head refiner. 4.00 

One night refiner. 3.00 

Four ladlers, at $2.75. 11.00 

Man fishing ingots. 1.50 

Boy dumping molds.75 

Boy removing specks from ladles while pouring.75 

Man wheeling copper to packing-room. 1.50 

One laborer about furnace. 1.50 

One head packer. 2.50 

Two assistants, at $1.50. 3.00 

Miscellaneous expenses of packing, paint, stencils, etc.. .65 

Cost of pumping water for boshes. 1.15 

Proportion of day and night foreman. 3.00 

Proportion of expense during Sundays, and other delays. 1.44 
Proportion of assaying necessary for control of operation. 1.12 

Grand total.$67.06 

Cost per pound, ’2794 cts. 

This agrees closely with the actual cost of running large 
refining-works where prices closely approximated those assumed 
in this estimate j being just three-tenths of a cent, including gen¬ 
eral expenses. 



















CHAPTER XV. 


REFINING COPPER WITH GAS IN SWEDEN. 

At Atvidaberg,* in Sweden, a regenerative gas plant is used 
to heat the small reverberatory furnace in which the cement cop¬ 
per, obtained from cupriferous pyrites by the use of the Hen¬ 
derson extraction method, is first made into blister copper, and 
eventually refined upon the same hearth, though in a second 
operation. 

This plan of using the same furnace for the making of both 
blister copper and refined copper can by no means lie recom¬ 
mended, as the impurities which remain within the furnace from 
the first operation are sm*e to hinder the more delicate end-opera¬ 
tion. But where the product is small, as at Atvidaberg, it is 
sometimes necessary to work with imperfect apparatus, and the 
small proportion of sulphur in the cement copper removes the 
principal objections to this plan of procedure. 

The small scale of working here practiced cannot be reeom - 
mended, as it is neither conducive to economy nor to a high grade 
of product; but the successful employment of a gas-producer in 
copper-refining is so interesting and instructive, and bears so 
strongly upon the conditions existing in many parts of our own 
country, that I think it well worth while to embrace the oppor¬ 
tunity that has presented itself of describing it minutely, and 
with detailed working-drawings to illustrate the apparatus em¬ 
ployed. 

The cement copper is charged in a moist state, containing 50 
to 60 per cent, copper, with refinery-slags and a small amount of 
roasted, high-grade matte, and a considerable proportion of 
charcoal, to prevent the oxidation of the fine particles of metallic 
copper. 


* Mr. Paul Johnson, of Sweden, an experienced copper-metallurgist, has 
kindly furnished this description of work at Atvidaberg. 





364 MODERN AMERICAN METHODS OF COPPER SMELTING. 


A low-grade blister copper is produced herefrom, carrying 
only some 92 per cent, copper, and thus far inferior to any blis¬ 
ter copper that is produced in this country in a reverberatory 
furnace. The grade of this copper could be-easily improved by 
lengthening the period of oxidation. But it has been found more 
economical to throw more work on to the refining part of the 
operation, and produce a lesser proportion of rich slags from the 
preparatory process. The quality of the refined copper is entirely 
satisfactory, as indeed it ought to be, considering the favorable 
composition of the ores from which it is made, they being 
mostly cupriferous iron-pyrites, which is first burned in kilns to 
utilize the sulphur contents for acid manufacture. 

The gas generator is fired entirely with a very cheap and 
poor quality of fuel, consisting of refuse wood from building 
operations, ends of scantling, slabs, limbs of trees made into 
fagots, and similar waste material, and the gas is purified from 
tar by direct contact with water. 

THE BLISTER PROCESS. 

The operations here described were executed in the year 1889, 
and starting with a cold gas-producer, and furnace hearth, the 
latter merely having been slightly warmed by a small wood fire 
upon the hearth. 

This small fire was kept upon the hearth about sixteen hours 
before filling up the gas-producers, the flame being allowed to 
pass out through the regenerators on either side. 

At the expiration of this time, and at about 6 a.m., the fire in 
the gas-generator was kindled, the latter within the next three 
hours being filled nearly to the top with the refuse wood already 
mentioned. 

By 10 a.m., four hours after the kindling of the fire in the 
generator, it was considered safe to let the gas into the furnace, 
it having hitherto passed off into the air. Any carelessness in let¬ 
ting the gas into the furnace before all air is driven out of the 
generator might result in a serious explosion. The gas is shifted 
from one regenerator to the other every 10 minutes by means of 
a valve, and by 6 : 30 pm., 124 hours from starting, the hearth of 
the furnace has reached a bright yellow heat. 

The bridge-wall and other exposed parts were then repaired 
in the customary manner by tamping into the burnt-out cavities 


IMPROVEMENT OF THE GENERATORS 



A.N E> 

SUBSTITUTION OF SURFACE CONDENSERS 

FOR 'THE: 

GAS FURNACES AT ATVIDABERG. 


SCALE 



















































































































































































































































































































































































































































































































































































































































































































































































































GAS GENERATOR 


:nerator 


yjn^dL 


mmitnnmiiiiiiiiiiiiiiinnn 




GAS OUTLET PIPE 
N TO FURNACE 


blowing-off pipe for con¬ 
ducting AWAY THE GAS AT BLOW- 
INO IN ANO BLOWING OUT 


Generators and Condensers 

- FOR - 

ATVIDABERG GAS FURNACES. 


12 Feet 



































































































































































































































































































































































































































































































































































































































































































































































































■ 



































































































































































REFINING COPPER WITH GAS IN SWEDEN. 


365 


crushed quartz, sieved through a screen with eight meshes to the 
linear inch, and at 8: 15 p.m., 14J hours from the start, the 
furnace was hot enough to begin charging. 

Nine cubic feet of charcoal fines (a totally valueless material 
where charcoal is used, and that can be obtained without cost) 
was first dumped upon the furnace-hearth, then 300 pounds of 
thoroughly roasted copper matte containing about 50 per cent, 
copper, then 600 pounds of refinery slags, containing 40 to 60 
per cent, copper, then some two cubic feet of charcoal again; on 
top of this came 1,650 pounds of cement copper, and last of all, 
f>00 pounds more of roasted matte, after which the doors were 
luted and the gas turned on again. 

The great bulkiness of the cement copper requires that, in 
this small furnace, the charging should be done in two separate 
operations. At 9 : 45 a.m., 13J hours after charging, the material 
was sufficiently fused down to admit the addition of the remain¬ 
der of the charge. Four cubic feet of charcoal fines were first 
thrown upon the half-molten bath, then 1,500 pounds cement 
copper, then 300 pounds each of roasted matte and refinery slags, 
and, last of all, about 40 pounds of dirty cement copper, from 
the straw filters of the precipitating tanks. 

The working-door was luted up at 10: 05 a.m., and at 2 p.m., 
after four hours’ firing, the charge was sufficiently fused to admit 
of the first slag-skimming, which was conducted in the custom¬ 
ary manner. At 3 : 30 and 4 : 45 p.m., slag was again skimmed in 
small quantities, the charge still being far from liquid all through, 
and much of it still sticking to the hearth. 

As the blister copper is here tapped into iron molds (an excel¬ 
lent plan which cannot be too highly recommended to our own 
smelters for its cleanliness and economy), these are now heated 
with slag from a fourth skimming at 5 :45 p.m., at which time it 
was found that the bottom was getting clean, and that bubbles 
were beginning to rise through the molten mass, showing that 
the chemical reactions between the sulphides and oxides present, 
as well as between the carbon (charcoal) and oxides were rapidly 
progressing. At 6 : 20 p.m. a considerable quantity of tolerably 
liquid slag was skimmed, and a thorough stirring of the bath with 
a stout iron hook took place, to free the bottom and assist in 
breaking up the still unfused masses. A slight blast was now 
forced through openings in the fire-bridge to cool the overheated 


3G6 MODERN AMERICAN METHODS OF COPPER SMELTING. 


brick-work in that portion of the furnace, and at 6 :40 p.m. slag 
was again skimmed. At 7 p.m. the surface of the copper was 
skimmed tolerably clean of slag, though a considerable him of 
matte still floated upon it, and the blast was now let on through 
two blow-holes in the rear of the furnace to hasten the oxidation 
of the sulphur and iron. Sometimes, instead of using blow-lioles, 
a tuyere is introduced into a small door opposite the charging- 
door, and there luted in place. 

At the same time the admission of air to the gas-producer was 
increased so as to make the flame more oxidizing, and permit it 
to play more freely over the whole extent of the bath. 

Between 7 and 9 : 20 p.m., four skimmings were made, and at 
the last one, the bath was again skimmed clean, and a test taken 
in a small ladle, which showed a pretty even surface. 

The sulphurous acid gas is escaping rapidly in a multitude of 
flue bubbles (German “Braten”), and this action increases in 
violence until globules of molten copper are thrown out through 
the working-door. The slag, which at first was dense, now 
becomes pasty and full of bubbles. 

Tests taken every few minutes showed a disposition to rapidly 
become thinner and more concave, until at 10: 10 p.m. they as¬ 
sumed their proper form, i.e., swelled up with a hollow in the cen¬ 
ter like a baker’s roll, the bottom portion, when broken, showing 
a reticulated surface. 

The blister copper is now tapped at once, after a few moments 
of strong heating, into iron molds, formed on the bottom by a 
large iron plate, while the sides are made of strips of iron shaped 
like a triangular gutter, and laid on their open side, the apex of 
the triangle being uppermost. Small cross-divisions of sand are 
made between these parallel sides, and the sand is covered with 
a thin layer of clay mortar to strengthen them, and which must 
be thoroughly dried before the metal is tapped into them. 

The tapping of the blister copper is accompanied by a strong 
evolution of sulphurous and sulphuric-acid gases, and requires 
some skill in its management, being guided and controlled in 
its impetuous course by long wooden poles in the hands of the 
furnace-men. As in the common English and American practice, 
the pigs are broken apart at their junction while still almost 
white-hot, and as soon as the outside of the pig has become 
strong enough to allow it to be pried upon with a heavy iron bar. 


REFINING COPPER WITH GAS IN SWEDEN. 


367 


At this stage, the blister copper is very red-short and brittle, 
but it' the critical moment is neglected, it becomes tough and 
unmanageable, necessitating a most laborious and expensive 
recourse to cutting apart, with chisels. A little sand or line 
charcoal is thrown upon the necks of the pigs to keep them hot 
until the pig has solidified enough to bear handling. 

The furnace is now scraped out clean, and the sides and 
bridge mended with crushed quartz in the usual manner, a long 
plug of wood being first driven into the tap-hole, and thoroughly 
packed with damp sand, so that it soon carbonizes, and becomes 
a plug of charcoal which is easily penetrated by the tapping-bar. 
On this small furnace, about 140 pounds of quartz are used for 
repairs after each charge, and this is heated strongly for about 
an hour. 

Only one charge is made in twenty-four hours, the actual time 
taken for the operation being about 21J hours, and the furnace- 
gang consisting of one head smelter, one assistant, and one man 
at the generator, all on eight-hour shifts. 

The consumption of fuel in this operation is very difficult to 
estimate, as every scrap of waste wood is used, in the shape of 
old roots, branches, ends of sawn-off timbers, etc.; also sawdust. 
About 850 cubic feet of waste limbs and 400 cubic feet of waste 
wood were used in twenty-four hours, but as this w r as all esti¬ 
mated by measure, and as from its irregular shape, the inter¬ 
stices bore an enormous proportion to the amount of solid wood 
employed, it is evident that a very reasonable consumption of 
fuel took place. 

The taking of tests from the bath, and the judging of the 
forwardness of the operation therefrom, are difficult and deli¬ 
cate, and depend largely upon experience. As the blister copper 
in our large blister-furnaces presents exactly the same series of 
changes, and as inexperienced men are constantly perplexed and 
mystified by this matter of tests, I will give a brief description 
of the appearance of these tests at Atvidaberg, as the same de¬ 
scription will apply equally well to our own conditions. 

The tests are taken at most works in a small ladle about 14 
inches in diameter by 4 inch deep. 

A test taken early in the operation, and before the process of 
oxidation has advanced very far, is level at surface, and shows a 
dull gray fracture, with few T shining points. 


368 MODERN AMERICAN METHODS OF COPPER SMELTING. 

As the oxidation of the sulphur progresses, the assay seems 
to spread out thinner, and on fracture shows less dullness, and 
a multitude of small bubbles begins to appear. 

Still farther on, the bubbles begin to enlarge, becoming the 
size of small peas, while the surface of the test rises and becomes 
more convex. This increases till it looks very much like a 
baker’s roll, and shows an indescribable vitreous luster in the 
interior of the bubbles on fracture, when the blister process is 
complete, and the copper is ready to tap. If the oxidation were 
carried further, there would not only be a heavy loss of copper 
in the slag (there is a much less loss in the refining operation 
later, as the slow melting-down of the blister copper assists 
greatly in oxidizing the last traces of impurities without much 
slagging of copper), but the blister copper would lose its valu¬ 
able quality of excessive “ red-shortness ” by which we are enabled 
to easily break the pigs apart, and other practical disadvantages 
would occur. 

But if, in spite of these drawbacks, the oxidation of the cop¬ 
per is continued, the surface of the test becomes very convex, 
and finally it bursts, and, as the smelters say, “the worm crawls 
out,” by which they mean that the test “ spits,” or has an out¬ 
growth of molten copper on the surface, which looks like a worm, 
and is identical with the common “ spitting ” of a large silver but¬ 
ton when cooled too quickly after cupellation. 

Of course, as soon as the impurities in the blister copper are 
thoroughly oxidized, and indeed long before this point, the cop¬ 
per itself begins to oxidize rapidly, and to form a silicate of 
copper, taking up quartz from the hearth sides and fettling. I 
remember one instance in my early practice, when I had engaged 
a new refiner, and was called away just toward the close of the 
. oxidizing stage, but anticipated no trouble, as the man brought 
good recommendations. When I returned in five or six hours I 
was informed that the copper was all sinking away and going to 
slag, as was indeed the case, the bath in the furnace having 
shrunk to infinitesimal dimensions, while the whole shed was 
filled up with blood-red slag. It seems that the new refiner had 
kept on oxidizing, expecting to see some peculiar appearance of 
the test which he was used to in refining the very impure copper 
that he had always worked on. Our copper being from a wet 
process, and of the highest grade of purity to begin with, failed 


-12 0 - 





c'_ 





IMPROVED BRUECKNER’S CYLINDER, AS USED FOR ROASTING COPPER ORES. 

Side Elevation. 


Front Elevation. 
(Fire-box removed.) 



























































































































































































































































































































































































































































































































REFINING COPPER WITH GAS IN SWEDEN. 


369 


to show this peculiar phenomenon, which he termed “The 
bloomin’ o' the Butt,” if any one knows what that means, and he 
had patiently kept on oxidizing, regardless of the ominous lessen¬ 
ing of the bath. The slag was all put back, with some charcoal 
and a little high-grade matte, which furnishes the best reducing 
agent that we have in the reverberatory furnace, and in the 
course of a few hours the copper was again obtained, and this 
time in a proper state of purity. 

THE REFINING OF THE BLISTER COPPER IN GAS FURNACES AT 

ATVIDABERG, SWEDEN 

The operation of refining at Atvidaberg is conducted in the 
same furnace that is used for the blister process. 

1 need hardly say that this is neither scientific nor economical, 
and is simply done on account of the small production and the 
fact that where labor and fuel are so cheap, and the capital of the 
owners is limited, it is considered better to delay the refining 
operation slightly than to go to the heavy expense of a separate 
refining furnace. 

Of course, if there were much arsenic or other seriously 
injurious foreign substances in the blister copper, it would be 
practically impossible to produce a high grade of copper in this 
manner. But as the metal is remarkably free from the more 
dangerous impurities, this practice simply delays the refining 
process a few hours, as every atom of sulphur, iron, or other 
impurity resulting from the blister process, and which is certain 
to cling to the hearth and sides of the furnace in perceptible 
quantities, has to be oxidized and eliminated, either up the stack 
or in the slag, before refined copper of the proper quality can be 
produced. If it were practicable, it would be very much better 
to accumulate a large stock of blister copper before refining at all. 
Then to run the furnace solely on refined copper until the supply 
of blister is exhausted, by which time sufficient cement-copper and 
matte would have accumulated in stock for another blister cam¬ 
paign. The sole objection to this plan is the amount of capital 
it would take to pay the running expenses of the works and 
mines while the blister copper for a campaign was accumulating. 

The charge of blister copper is very small, only about 5,000 
pounds, and in a furnace in normal condition this is fused down 
in about four hours. The bath is then skimmed clean, the 


370 MODERN AMERICAN METHODS OF COPPER SMELTING. 


amount of slag being very small, owing to the unusual purity of 
the blister copper. 

A light blast is turned upon the surface of the molten metal 
by means of a small tuyere introduced through a door opposite 
the working-door, and the copper is at the same time kt flapped ’ 
constantly with a small rabble in the usual way. Of course the 
object of this stage is to expose the molten copper to the action 
of the air as rapidly as possible, and thus promote quick oxida¬ 
tion of the impurities that it contains, for the whole process of 
copper refining is based upon the fact that the impurities that 
are commonly contained in copper oxidize more easily and quickly 
than the copper itself. If they happen to possess a lesser chem¬ 
ical affinity for oxygen than the copper itself, they will, of course, 
remain unoxidized. A familiar example of such unoxidizable 
substances are silver and gold, which remain alloyed with the 
copper throughout the refining process, and indeed could, theo¬ 
retically, be separated from the copper by oxidizing and slagging 
it off, leaving the precious metals behind, as in the cupellation of 
lead. In practice, this method has not been found economical, 
except under certain rare conditions, where it plays an important 
part in the separation of these metals. 

I doubt very much if the air-blast from the tuyere striking the 
surface of the copper produces any very marked acceleration of 
the oxidizing process. I have more than once tried it under 
similar conditions in the ordinary English method of refining as 
practiced in this country, but could not see that it made any per¬ 
ceptible difference, and am inclined to think that it is merely a 
relic of the old-fashioned German refining method, where the 
tuyere was necessary to produce an air-current on the surface of 
the molten bath, there being no arch over the German refining 
hearth, and consequently no strong, natural air-current over the 

surface of the metal as there is where a reverberatorv furnace is 

«,• 

used. 

But the degree of energy and skill with which the u flapping” 
is executed has a very marked effect upon the time necessary for 
this stage of the operation. It is most difficult, violent, and 
exhausting labor, and requires much tact and experience to strike 
the bath with the proper force and just at the proper depth to 
break it at that point into a shower of drops, which fall over a 
large area, and at the same time send out a large number of con- 


REFINING COPPER WITH GAS IN SWEDEN. 


371 


centric wavelets of copper, that present a greatly increased sur¬ 
face to the action of the air-current that is hurrying 1 over the sur- 
face of the hath to gain the chimney. 

At Atvidaberg, this stage of the process usually occupies 1J 
hours, at the end of which period a test taken in the small ladle 
should show a very coarse, crystalline, light-red fracture, the 
small bubble in the center being a bluish-black instead of the 
reddish-brown hue that it showed during the early part of the 
oxidizing period. 

The impurities are now nearly all removed, or else exist in 
the copper in the shape of oxide, while the metallic copper proba¬ 
bly contains a considerable amount of suboxide of copper in 
solution. 

The bath is skimmed clean, and the “poling” now begins, in 
order to lessen the amount of suboxide of copper (with which it 
was necessary to saturate the metal in order to thoroughly oxi¬ 
dize all foreign elements), as well as to reduce the foreign oxides 
dissolved in the copper. As these are reduced, they act in three 
different ways. Such as are at all volatile, pass off in gas. A 
considerable portion of the fixed oxides is taken up by the slag 
formed during the operation. While a third and very small 
portion is reduced back to metal and remain in the copper as 
impurities, iron being the principal of these. 

The poling operation is divided here, as elsewhere, into two 
stages: 

Dense poling and 

Tough poling. 

A large birch pole is thrust into the working-door, its butt 
being forced down into the molten bath by raising forcibly its 
thinner end which projects into the air, using the upper edge of 
the furnace door as the fulcrum, while the pole is retained in 
position by a piece of notched plank, set under its projecting end. 
The ebullition of gases is very great, and a rapid reduction takes 
place in the copper, while currents are established in every direc¬ 
tion, so that all the metal in the furnace is rapidly brought under 
the influence of this powerful reaction. 

The crystalline texture of the fractured test becomes of a much 
finer pattern, and the color much fighter and more pinkish, while 
the bubble in the center becomes rapidly smaller and more yel¬ 
low, and soon disappears. When these reactions are fairly estab- 


372 


MODERN AMERICAN METHODS OF COPPER SMELTING. 


listed, and tlie test is seen to take on a dense, fibrous texture 
from below upward, the stage of “ dense poling ” is considered at 
an end. 

It usually takes about forty-five minutes, during which time 
the slag is skimmed several times, and as it now largely consists 
of a subsilicate of the oxide of copper which is too thin to skim 
off, sand is thrown on the surface of the bath to thicken the 
slag. 

At the beginning of the “ tough poling/’ a barrel of clean, 
selected charcoal is thrown upon the clean surface of the bath, 
and a fresh pole introduced. Tests are now constantly taken, 
the changes in the quality of the copper, though chemically very 
slight, being now both physically and commercially very impor¬ 
tant, and succeeding each other with extraordinary rapidity. 

The fracture of the test is now becoming pinkish and fibrous, 
and minute pearly globules begin to appear under the magnifier, 
while the toughness of the metal increases in a remarkable 
manner. 

As the process progresses, the even rows of fibers begin to 
disappear, and an irregular, very finely grained fiber replaces 
them, while the fracture looks more silky and the toughness 
increases. 

In tw r o or three minutes from this time, the pearls suddenly 
become distinct, the beautiful rosy-pink of refined copper appears, 
and the test becomes so tough that, after nicking it with a chisel, 
it can be bent back and forth many times in a vise without 
breaking. 

The pole is now withdrawn, fresh charcoal is spread over the 
bath to entirely exclude the air, and the heated and clay-washed 
ladles are brought to the door. 

The ladling of this small charge of 5,000 pounds or less took 
over an hour, having to be interrupted several times to pole the 
copper, and well exemplifying the claim I have so often made for 
large furnaces and large charges, that it is infinitely more diffi¬ 
cult to handle small quantities of metal, as the slightest mis¬ 
chance, or undue splashing about of the copper by the ladles, 
causes oxidation, and gets it u out of set.” 

When we are ladling a proper amount, say 25,000 to 35,000 
pounds of copper in one operation, we seldom have to put in a 
pole more than once or twice until w r e come nearly to the end of 


REFINING COPPER WITH GAS IN SWEDEN. 


373 


the ladling, and are dealing with something like the quantity that 
they begin with in Sweden. 

And in order to be sure that there shall be no mistake in the 
quality of the copper, I have usually made a practice of closing 
the operation as soon as it becomes difficult to keep the metal u in 
set, ’ and ladling out the little copper that remains in the furnace 
into sand beds, to be thrown back into the furnace at the next 
refining. There is no waste in this, and practically no expense, 
the sole drawback being the couple of hundred dollars invested 
in the extra amount of copper that is thus kept circulating in the 
process, and gets into market twenty-four hours later. With 
interest at 10 per cent, per annum, the cost of this practice 
would be about one-half cent per day, and allowing even 10 
cents for the amount of fuel necessary to resmelt it (for the 
labor costs nothing, it being all done under contract, and the 
extra labor of throwing a few ingots back into the furnace not 
being heeded by the men), it will be seen that the cost is not 
to be considered in comparison with the very serious trouble 
and expense arising from sending out copper of unequal quality. 

I mention these details, as I have heard this practice denounced 
as wasteful and extravagant, while 1 consider it a decided im¬ 
provement, if a small one. 

The refined copper produced at Atvidaberg amounts to about 
90 per cent, of the blister copper charged into the furnace. Con¬ 
sidering the unusual purity of this blister, the amount of slag 
produced is excessive, which arises from two causes already men¬ 
tioned ; one being the very small charge used, a large charge 
giving a much smaller per cent, of slag to be resmelted, while 
the other cause is the practice of using the same furnace for both 
the blister and refining processes, by which the latter operation 
is prolonged and more slag produced. 


THE USE OF BASIC-LINED FURNACES FOR REFINING COPPER. 

The remarkable results obtained by Mr. Percy C. Gilchrist in 
England from the use of basic material for hearths and finings 
of blister furnaces have been fully stated in the chapter on the 
blister process. 

Encouraged by the unusual success that crowned his efforts, 
Mr. Gilchrist very naturally desired to apply his new ideas to the 
operation of refining copper. 


374 MODERN AMERICAN METHODS OF COPPER SMELTING. 


As lie states in his own paper on the subject, there is very 
much less chance for improvement in the refining process than 
in the blister process. For in the former, the impurities have 
already been mostly removed, and the amount of slag produced, 
even in ordinary furnaces, is very small. 

Still lie finds a most decided diminution both in the quantity 
and the copper percentage of the slag produced in basic furnaces 
during the operation of refining. And, as is quite as one 
would expect, he finds that the more impure the copper charged 
is, and consequently the longer the period of oxidation has to last 
in the refining furnace, the more useful does his basic fining 
prove to be. For on an acid hearth, the oxide of copper formed 
during the earlier stages of refining is constantly dissolving 
silica out of the hearth and fining, and augmenting tfie quantity 
of the slag. 

He does not find, however, that the arsenic or antimony is 
removed anymore quickly by the basic fining; rather the con¬ 
trary. 

«/ 

The practical question immediately arises, whether it will 
pay to apply this method to our refining furnaces here in the 
United States. 


My own opinion is, that under our present conditions the 
advantage gained would be so slight as to hardly pay for the 
change. 

This is because most of the copper that with us undergoes a 
refining operation is already purer than average English copper 
is after the end of the refining process. The reason of this con¬ 
dition of things is partly, that nearly all matte produced in 
the United States that is at all arsenical or antimonial is also 
sufficiently rich in silver or gold to warrant the separation of 
these metals, which is, of course, accompanied by the elimination 
of the arsenic and the production of a copper of the very high¬ 
est quality. 

Still another reason exists, which I hesitated to mention in 
the first edition of this book. But feeling myself fortified with a 
few more years of experience and observation, which only serve 
to make me more certain of what I knew before, I no longer 
hesitate to say that the reason why our American copper market 
is in such a crude condition compared with that of England, 
the reason why our refiners hesitate to deal in the dry way with 


REFINING COPPER WITH GAS IN SWEDEN. 


375 


arsenical material, and above all, the reason why onr grades of 
coppei are divided with such charming simplicity into merely, 
u Lake copper,” “Arizona copper,” and “Montana copper,” is 
that our consumers of copper are so ignorant of the peculiar¬ 
ities of different coppers, as well as of just what they need in the 
copper that they purchase for their own use, that many of them 
cannot foim an independent judgment of the quality of a given 
brand of copper by physical and chemical tests, and therefore 
are obliged to frequently buy a better copper than they need to 
make sure of getting one that is good enough. 

It is startling to English refiners to see our superb Lake 
copper used wholesale for making certain castings that would be 
just as good if an inferior metal were used, costing one to one 
and a half cents less per pound. 

Having refined copper for the open market myself for several 
years, I can speak intelligently on this point, and in more than 
one instance have been unable to introduce a good, fair casting 
brand of copper, as the manufacturers who tried it assured me 


that their foreman was unable to obtain sound castings from it. 
The extreme sensitiveness of copper to external influences was 
well exemplified in these cases, for when, by permission of the 
owners, our own brand of copper was shipped to them in some 
old “ Lake ” barrels, its quality was found to be so improved by 
the packing that the foreman had no fault to find with it. 

Until accurate physical and chemical tests are substituted for 
a mere glance at the color of the ingot or cake, and the manu¬ 
facturers have learned to buy copper just good enough for their 
work and no better than they need, there is little encouragement 
for refiners to trouble themselves to improve the quality of their 
product. 

So long as “ Arizona ” is bound to sell for a cent or more less 
than “ Lake,” regardless of how suitable it may be for the in¬ 
tended purpose, just so long will it be idle for the refiner to 
expend time and money in making a better quality of “ Arizona.” 

But this crude state of affairs cannot last long, for Americans 
are not likely to remain indifferent to a matter that affects their 
profits so largely. 

It is for the refiners to lead the way, and to urge upon the 
manufacturers the importance of adapting the quality of the 
copper that they buy to the purpose for which it is intended, and 


376 MODERN AMERICAN METHODS OF COPPER SMELTING. 

not use Lake copper with its superb malleability and high con¬ 
ductivity, for making castings. 

When this matter is better understood, the inferior coppers 
will no doubt be much more generally used, and the present wide 
margin in price between them and Lake copper will be reduced 
to much narrower limits. 


CHAPTER XVI. 


TREATMENT OF GOLD- AND SILVER-BEARING COPPER ORES. 

A very few words may serve to indicate the present practice 
in the separation of the precious metals from copper. The older 
processes employed for this purpose were by far the most com¬ 
plicated and wasteful operations known to metallurgy, and it is 
only since the discovery and introduction of the various u wet ” 
processes that any but the richest coppers could be advanta¬ 
geously treated for the precious metals. 

The Ziervogel process has only been successful in a few 
isolated cases, and demands such pure material and such skill in 
manipulation as to debar its use in ordinary instances, nor does 
it provide for the extraction of gold. 

It is indisputable that the electrolytic methods are rapidly 
advancing to the front in the treatment of gold- and silver-bear¬ 
ing metallic copper, and have the great advantages of producing a 
copper of the best quality, but can only be profitably employed on 
matte carrying at least $30 per ton in precious metals and re¬ 
quire a bulky and extensive plant. 

The new Hunt & Douglas method, as applied to copper ores 
or mattes, seems to fill the gap more completely than any previ¬ 
ous invention. By this method, the copper is extracted from the 
ore or matte after a very imperfect roasting, and being precipi¬ 
tated as a dioxide by sulphurous acid generated from pyrites, it 
is decomposed by about one-half its weight of metallic iron, the 
resulting cement being fit for immediate refining. The copper 
is obtained in a state of absolute purity even in the presence of 
arsenic and antimonv, while the residues, containing every trace 
of the gold, silver, and lead originally present, may be smelted 
with lead ores in a blast-furnace. The process has long passed 
the experimental stage, and offers advantages peculiar to itself 
and unshared by any other. 

The ease with which the small amount of gold sometimes 


378 MODERN AMERICAN METHODS OF COPPER SMELTING. 


present in cupriferous pyrites may be won is not realized by all 
copper smelters, although the method is extensively practiced in 
this country, as well as at Swansea and in Chili. 

Owing to its great affinity for metallic copper, the gold con¬ 
tained in white metal may be concentrated into a very small 
bulk of the former by exposing the pigs of matte to a slow, oxi¬ 
dizing fusion, exactly as in the process for making blister cop¬ 
per. The operation, however, is interrupted as soon as a certain 
quantity of metallic copper is formed, when the furnace is tapped, 
and the product—now advanced to pimple metal , or even regale ,. 
from 82 to 88 per cent.—being examined, bottoms of metallic cop¬ 
per will be found under the first few pigs. This is the method 
pursued in making best selected copper ■ for not only does the 
small quantity of metallic copper extract the gold, but also the 
greater part of other foreign and injurious substances—such as 
arsenic, antimony^ tellurium, tin, etc. The proportion of bottoms 
formed must vary with the quantity of gold present; in some 
instances, even a repetition of the processes being required to 
fully extract the more valuable metal. Silver is but slightly con¬ 
centrated by this operation, as will be observed from the follow¬ 
ing assays made under the author’s direction, want of space for¬ 
bidding fuller details of this important process: 


Assay of original 
white metal. 

Propor¬ 
tion of 
bottoms 
formed. 

Assay of bottoms. 

Proportion thus 
extracted. 

Assay of residual 
pimple metal. 

Gold. 

Silver. 

. Gold. 

Silver. 

Gold. 

Silver. 

Gold. 

Silver. 

Ounces. 

0-64 

2-37 

0-11 

Ounces. 

93-3 

16-6 

Percent. 

6-4 

9-0 

5-4 

Ounces. 

9-60 

19-10 

1-73 

Ounces. 

213-4. 

36-2 

Per cent. 

93-7 

90-2 

88-4 

Per cent. 

14-8 

18-5 

Ounces. 

0 • 030 

o-iio 

0-012 

Ounces. 

78-7 

14-2 


In examining this table, it must be remembered that a consid¬ 
erable concentration has taken place in the matte itself as well as 
in the copper bottoms, so that the results do not seem to agree; 
but the figures given are sufficient to indicate the general results 
of the process. Unless the furnace bottom is already well satu¬ 
rated with auriferous metal, a heavy loss in gold must be expected. 


























CHAPTER XVII. 


THE BESSERMERIZING OF COPPER MATTES.* 

While the reader must he referred to Professor Egleston’s 

pamphlet, as well as to the literature of the future, for all details 

pertaining to this new and interesting innovation, the present 

treatise would be incomplete without a few remarks upon a process 

which promises to become of great importance when introduced 

where the conditions are suitable for its application. So many 

new and valuable improvements have been greatly injured and 

retarded by their miscellaneous and improper application that a 

few words of advice from one who witnessed the construction and 

starting of the first successful American copper-Bessemerizing 

plant may be of value. While there is no doubt of the technical 

success of the process as perfected by M. Manhes, and of the plant 

as constructed in this country under the direction of his pupils, 

it is onlv under certain conditions that its real usefulness can 
€/ 

assert itself, and any attempt to apply it to all and every variety 
•of circumstances would certainly result disastrously. 

The Bessemerizing plant, as constructed at the works of the 
Parrot Silver and Copper Company at Butte City, and observed 
by the writer at its commencement, was adapted to two different 
duties: 1st. To receiving copper matte of a low grade—from 15 
to 40 per cent.—and bringing it up to white metal—75 per cent.; 
or, 2d. To bringing white metal up to a very pure blister copper. 

The impossibility of producing metallic copper from poor 
matte at one continuous operation is quite evident, as, aside from 
the difficulty of dealing with the great quantity of slag formed 
from the iron and other foreign bases contained in the low-grade 
matte, the amount of metallic copper produced therefrom would 
be too small for manipulation. For instance, the usual charge 
—2,000 pounds of a 20 per cent, matte—would yield less than 

* See School of Mines Quarterly for May, 1885, for paper on this subject 
by T. Egleston. 




380 MODERN AMERICAN METHODS OF COPPER SMELTING. 

400 pounds of blister copper, a quantity far too small to submit 
to any blowing operation in a converter. 

This is especially the case in M. Manhes’s converter, where the 
tuyere orifices are situated at some distance above the bottom of 
the vessel. This latter peculiarity has been found an essential 
element of success; for, whereas in iron, the whole contents of 
the converter are homogeneous, the blast traversing the entire 
mass of metal, and oxidizing the impurities, which may be re¬ 
garded as distributed equally throughout the molten iron, so that 
the whole product gradually becomes pure without any divis¬ 
ion into a finished and a still uncompleted portion—in treating 
copper matte above 75 or 80 per cent., the liquid metal that until 
that point has been homogeneous throughout, must then begin to 
separate into two portions—namely, sulphide of copper, and me* 
tallic copper that has been deprived of its sulphur by oxidation. 
As the process continues, the latter product augments in quan¬ 
tity, while the former decreases, until the last atom of sulphur is 
removed. Were the tuveres at the bottom of the converter, the 
metallic copper would soon chill and obstruct them, and it was 
not until M. Manhes raised them to such a height as to allow the 
quiet subsidence of the metallic product below their inlets, that 
he attained complete success. It is necessary, however, that a 
sufficient amount of copper be present to support the superin¬ 
cumbent layer of liquid matte above the tuyere openings, so that 
the blast may traverse a molten and oxidizable product to the 
last, and thus generate sufficient heat to maintain the entire mass 
in a liquid condition. 

Experience has shown that upon introducing a matte contain¬ 
ing from 72 to 75 per cent, of copper into the converter, the pro¬ 
cess advances with great rapidity and completeness, while a matte 
of 60 or 65 per cent, requires several times as long for its oxida¬ 
tion. On the other hand, a low-grade matte of even 15 or 20 per 
cent, advances with satisfactory speed to the condition of white 
metal—from 70 to 75 per cent.—and there stops or continues 
very slowly. The practice has, therefore, been adopted of inter¬ 
rupting the oxidation of the low-grade matte at the point indi¬ 
cated, pouring it out of the converter, that it may separate from 
the slag, and subsequently completing the process in a second 
vessel, the products of two or more u blowings ” of poor matte? 
being united to form a single charge for blister copper. 


BESSEMERIZINGr COPPER. 


381 


It is therefore necessary for economy to have two sets of 
converters, and while three converters are required for a single 
operation, five, or possibly four, converters are sufficient for the 
complete process. A converter will usually stand from eighteen 
to twenty-four blows (twenty-four hours) without repairs, so that 
for the single operation, one converter is undergoing repairs, the 
second is drying, while the third is in use. 

In 1 1 ance, a separate cupola is used for melting the matte 
foi the converter ; but the Parrot Company has found it feasible 

rectly from the ore blast-furnace to the con¬ 
verter. 


No fuel is required to keep up the temperature in the con¬ 
verter while working on low-grade matte; but the operation for 
blister copper requires the occasional use of a few pounds of coke 
to keep up the necessary high temperature. 


While the construction of the converter plant is simple, the 
management of the same requires much care and experience* 
The appearance of the flame issuing from the mouth of the 
vessel is of little value as a guide, owing to its changeable color 
from the various foreign constituents of the matte. The tuyeres 
require constant opening with an iron rod, taking one man’s 
whole time. 


The lining of the boiler-iron converter is of crushed quartz 
(or pure siliceous sand), mixed with enough plastic fire-clay to 
hold it together. It is rammed in large balls, the original shape 
and size of the interior vessel being obtained from an oil barrel, 
used as a core, about which the lining is rammed. The same 
material is used for repairs. A cylinder blowing-engine supplies 
the blast, which is much less powerful than in ordinary Bessemer 
work, the height of the liquid column of metal being only a few 
inches, and the entire charge not exceeding 2,200 pounds. 

Any attempt at estimating the saving effected by this opera¬ 
tion under any given circumstances would be futile, as the pro¬ 
cess, although satisfactory to its owners, and thoroughly success¬ 
ful in the opinion of the author—speaking as a spectator—is still 
under constant improvement, and when stripped of its crudities 
and adapted to American conditions will give very different 
results from those obtained at its first introduction. 


* The Parrot Company’s plant was erected by pupils of M. Manlies. 




382 MODERN AMERICAN METHODS OF COPPER SMELTING. 

There is every reason to believe that its capacity will be 
greatly increased, and, as even in its present state it can show a 
great saving in fuel and labor above any of the older methods, 
there is little doubt that it will, ere long, be recognized as an 
essential feature of every large copper plant, except where very 
cheap fuel or other peculiar conditions neutralize its advantages. 
The elimination of arsenic and antimony by this operation was 
highly satisfactory, as far as the author’s observations extended. 
Whether an undue loss of silver by volatilization may also occur 
in argentiferous mattes, yet remains to be decided. The slags 
from the Bessemerizing of low-grade mattes form a welcome basic 
flux in the ore-furnace, while the lining of the converter is par¬ 
tially protected from their corrosive influence by the feeding of 
pulverized siliceous ores through the tuyere-holes with the blast. 

Latest advices from the President of the Parrot Company 
report great improvements in the capacity and economy of the 
process. 

A simple set of converters now produces 50,000 pounds of 99 
per cent, copper, daily, from 60 per cent, matte, and casts of 
2,400 pounds of pig-copper are now made from a single charge 
of matte of this grade. 

Since the publication of the above the Parrot works have 
enlarged and improved their Bessemer plant, but no statements 
of cost and results can be obtained from them, and the method 
has not gained ground in this country. 


THE END. 


INDEX. 


A 

Absorption of Copper by Refinery 
Hearths, 344. 

Accretions, Removal of, from Fur¬ 
nace Walls, 247. 

Advantages of Stall-roasting, 106. 

Affinities, Fournet’s Law of, 181. 

Agglomeration, The, of Fine Ore, 276. 

Agordo, Kernel-roasting at, 85. 

Air, Excess of, to be avoided m Calci¬ 
nation for Reverberatory Smelting, 
173. 

Air-preheating for Reverberatory 
Smelting, 325. 

Air-space in Stack Linings, 330. 

Ammonia, Effect of, on Cyanide As¬ 
say, 37. 

Anaconda, Bruckner’s Cylinders at, 
138. 

Anaconda Mine, Description of, 15. 

Anaconda Mine, Percentage of Ore in 
Copper, 17. 

Anaconda Smelter, Improvements in 
Reverberatories, 324. 

Anaconda, Use of Hot Air for Smelt¬ 
ing, 328. 

Analysis of Atvidaberg Black Copper, 
274. 

Analysis of Calcined Ore, 175. 

Analysis of Chills from Forehearth, 

200 . 

Analysis of Clifton Slag, 215. 

Analysis of Copper from Blister Pro¬ 
cess, 338. 

Analysis of Copper Queen Slag, 214. 

Analysis of Ely Pig Copper, 273. 

Analysis of Hearth Sand for Rever¬ 
beratories, 306. 

Analysis of Metallic Bottoms, 340. 

Analysis of Ore Knob Pig Copper, 274. 

Analysis of Rio Tinto Pyrites, 119. 

Analysis of Slag from Blister Process, 
338. 

Ansonia Brass & Copper Co.’s Method 
of Casting Refined Copper in Molds, 
359. 

Antimony, Effect of, on Cyanide As¬ 
say, 35. 

Antimony, Removal of, by Roasting, 

104. 


Antimony, Removal of, from Copper, 
356. 

Appearance of Roasted Ore, 85. 

Arch of Reverberatory Calciner, Con¬ 
struction of, 153. 

Arch of Reverberatory Calciner, Slat¬ 
ing of, 157. 

Arch of Reverberatory, Use of Dinas 
Brick in, 302. 

Argo, Preheating of Air for Rever¬ 
beratory Smelting at, 325. 

Argo Reverberatory Furnaces, Cuts 
of, 326. 

Argo, Reverberatory Practice at, 325. 

Arizona Copper, Purity of, 220. 

Arizona Mines, Description of, 21. 

Arizona Mines, Production of, 19. 

Arsenic and Antimony Removed by 
Calcination, 172. 

Arsenic, Effect of, on Cyanide Assay, 
35. 

Arsenic, Effect of, on Electrolytic 
Assay, 39. 

Arsenic, High Percentage of, in Many 
Brands of Blister Copper, 339. 

Arsenic in Heap-roasting, 75. 

Arsenic, Removal of, by Stall-roast¬ 
ing, 104. 

Arsenic, Removal of, from Copper, 
356. 

Asbestos Used for Backing Fore- 
hearth, 201. 

Ash in Coke, Per cent, of, 220. 

Ash-bed Deposits, 10. 

Ash-pit for Reverberatory Calciner, 
152. 

Assaying Copper, Description of 
Methods of, 33. 

Assaying Copper, Methods of, 29. 

Assays of Auriferous White Metal and 
Bottoms, 379. 

Assays of Parrot Co.’s Matte, 320. 

Atlantic Coast Beds, 7. 

Atlantic Coast Beds, Production of 
Copper from, 9. 

Atlantic Mine, Cost of Production, 

11 . 

Atlantic Mine, Description of, 11. 

Atvidaberg, Dense Poling at, 373. 

Atvidaberg, Refining Copper with Gas 
at, 363. 




384 


INDEX. 


Atvidaberg, Size of Refinery Charges 
at, 370. 

Atvidaberg, Tapping the Blister into 
Molds at, 366. 

Atvidaberg, The Blister Process at, 
364. 

Atvidaberg, The Consumption of Fuel 
in Blister Process at, 368. 

Atvidaberg, The Flapping during Re¬ 
fining at, 371. 

Atvidaberg, The Ladling of Copper 
at, 373. 

Atvidaberg, The Poling during Refin¬ 
ing at, 372. 

Atvidaberg, The Production of Copper 
at, 374. 

Atvidaberg, The Refining of Blister 
Copper at, 370. 

Atvidaberg, Tough Poling at, 372. 

Automatic Hearth Furnaces, 141. 

Automatic Hearth Furnaces with 
Movable Hearths, 146. 

Automatic Hearth Furnaces with Sta¬ 
tionary Hearth, 141. 

Automatic Sampling-machine, 30. 

Azurite, 3. 


B 

Ball-pulverizer, 128. 

Barren Flux, Use of in Matte Smelt¬ 
ing, 271. 

Bartlett’s Water-jacket, Cut of, 225. 

Basic Charges, Evil of in Reverbera¬ 
tory Smelting, 321. 

Basic-lined Furnaces for Refining, 374. 

Basic-lined Furnaces, The Use of, 339. 

Basic-lined Furnaces, Treatment of 
White or Pimple Metal in, 342. 

Batter of Stacks, 161. 

Battery Assay for Copper, 38. 

Battery Assay, Illustration of Appara¬ 
tus Used in, 41, 42, 43. 

Bessemerizing Copper, The Difficul¬ 
ties Encountered in, 381. 

Bessemerizing Copper, The Loss of 
Silver in, 383. 

Bessemerizing Copper, The Necessity 
of Two Converter Systems, 381. 

Bessemerizing Copper, The Position 
of the Tuyeres, 381. 

Bessemerizing Copper, The Rapid 
Concentration of Rich Mattes, 381. 

Bessemerizing Copper, The Size of 
Charge, 380. 

Bessemerizing Copper, The Value of 
Slags from, 383. 

Bessemerizing Matte, Experiments 
on at Orford Works, 334. 

Bessemerizing of Copper Successfully 
Introduced by Manlies, 380. 


Bessemerizing Plant at the Parrot 
Works, 380. 

Bessemerizing, The, of Copper Mattes, 
380. 

Bessemerizing, The, of Nickel Matte, 
296. 

Best Selected Copper, The Manufact¬ 
ure of, 379. 

Bismuth, Effect of on Battery Assay, 
38. 

Bismuth, Effect of on Cyanide Assay, 
36. 

Blast Apparatus, 265. 

Blast-furnace Apparatus, Modern, 
269; 

Blast-furnace, Height of, 206. 

Blast-furnace, Length of Time Re¬ 
maining Banked, 245. 

Blast-furnace, Ores Suited to, 185. 

Blast-furnace, Proper Slag for, 185. 

Blast-furnace, Size of Charging Doors, 
206. 

Blast-furnace Smelting, 184. 

Blast-furnace Smelting, General Re¬ 
marks on, 256. 

Blast-furnace Smelting, Resume of 
by Howe, 285. 

Blast-furnaces Constructed of Brick, 
226. 

Blast-furnaces, Cost of Smelting in, 
253. 


Blast-furnaces for Smelting Oxidized 
Ores, 208. 

Blast-furnaces, Late Improvements 
in, 286. 


Blast-furnaces, Matte 
271. 


Smelting in, 


Blast-furnaces, Size of, 208. 

Blast-furnaces, Treatment of Fine 
Ore in, 275. 

Blast, Hot, Use of in Copper Smelt¬ 
ing, 258. 

Blast-pipe, Construction of, 268. 

Blast Pressure, Effect of on Furnace 
Capacity, 257. 

Blister Copper, Analysis of, 338. 

Blister Copper at Atvidaberg, Amount 
Produced, 374. 

Blister Copper at Atvidaberg, The 
Dense Poling of, 372. 

Blister Copper at Atvidaberg, The 
Flapping Operation, 371. 

Blister Copper at Atvidaberg, The 
Ladling of, 373. 

Blister Copper at Atvidaberg, The 
Poling of, 372. 

Blister Copper at Atvidaberg, The 
Tough Poling of, 372. 

Blister Copper, Difficulty of Opening 
Tap-hole, 338. 





INDEX. 


385 


Blister Copper, Effect of Impurities 
on, 338. 

Blister Copper Refining at Atvida- 
berg, The Size of Charge, 370. 

Blister Copper, The Analysis of Slag 
from, 338. 

Blister Copper, The Making of, 335. 

Blister Copper, The Refining of, at 
Atvidaberg, 370. 

Blister Copper, The Tapping of into 
Molds at Atvidaberg, 366. 

Blister Copper, The Time Required 
for Making, 336. 

Blister Copper, The Weight of 
Charge, 335. 

Blister Furnace Process at Atvida¬ 
berg, The, 364. 

Blister Furnace, The Treatment of 
Cement Copper in, 347. 

Blister Process at Atvidaberg; The 
Consumption of Fuel, 368. 

Blowers, 265. 

Blowers, Number of Revolutions of, 
266. 

Blowers, Power Required by, 268. 

Blowing-in a Water-jacket Furnace, 
211 . 

Blowing-out of Brick Blast-furnaces, 
250. 

Bornite, 5. 

Boshes in Copper Furnaces, 207. 

Bottom of Refining Furnaces, 344. 

Bottom of Reverberatory, Cost of 
Constructing, 317. 

Bottom, The, of Orford Furnace, 232. 

Bottoms, Metallic, Containing Silver 
and Gold, The Treatment of, 379. 

Bottoms, Metallic, Containing the 
Precious Metals, Table of Results, 
379. 

Bottoms, Metallic, The Analysis of, 
340. 

Bottoms of Refining Furnaces, The 
Absorption of Copper by, 344. 

Breakers for Coarse Crushing, 127. 

Breaking of Ore by Hand-spalling, 52. 

Breaking of Ore for Heap-roasting, 41. 

Brick Blast-furnaces, 226. 

Brick Blast-furnaces, Blowing-out of, 
250. 

Brick Blast-furnaces, Estimate of 
Cost of, 251. 

Brick Blast-furnaces, Large, Cost of 
Smelting in, 254. 

Brick Blast-furnaces, Repairs on, 248. 

Brick Blast-furnaces, The Orford Fur¬ 
nace, 227. 

Brick Forehearths, 198. 

Brick Furnaces, Use of Water-tuy¬ 
eres in, 250. 


Brick-work, Estimate of, in Building 
a Reverberatory, 313. 

Brick-work in New, Large Reverber- 
atories, Estimate of, 331. 

Bricking of Fine Ore, The Cost of, 
279. 

Bricking of Fine Ore with Clay, 280. 
Bricking, The, of Fine Ore, 276. 
Bronze Tapping-ring, Improvements 
in, 286. 

Bruckner’s Cylinders, 136. 

Bruckner’s Cylinders at Anaconda, 

138. 

Bruckner’s Cylinders at Butte City, 

139. 

Bruckner’s Cylinders, Economy of, 

140. 

Bruckner’s Cylinders, Setting-up of, 
140. 

Brunton, I). W., Automatic Sampling- 
machine, 30. 

Brunton, D. W., Quartering Shovel, 
31. 

Brunton’s Automatic Calciner, 146. 
Buckstaves for Reverberatory Cal¬ 
ciner, 155. 

Building of Roast-heaps, 69. 

Butte City, Annoyance of, by Fumes 
from Roasting, 59. 

Butte City, Bruckner’s Cylinders at, 
139. 

Butte City Furnace, Capacity of, 204. 
Butte City Mines, 15. 

Butte City Mines, Production of, 
17. 

Butte City Ore, Silver Value of, 16. 
Butte Practice of Making Rich Matte 
at First Smelting, 320. 

C 

Calcination, Consumption of Fuel dur¬ 
ing, 180. 

Calcination, Matte-fusion Assay dur¬ 
ing, 174. 

Calcination of Manganic Sulphide, 

171. 

Calcination of Pulverized Ore and 
Matte, The, 123. 

Calcination, Table of Results of, 178. 
Calcination, The Avoidance of Excess 
of Air during, 173. 

Calcination, The Cost of, 179. 
Calcination, The, of Arsenical and 
Antimonial Ore, 172. 

Calcination, The, of Zinc-blende, 171. 
Calcination, The Use of Charcoal in, 

172. 

Calcination, The Ziervogel Method of, 
171. 

Calcination, Varieties of, 46. 





INDEX. 


386 


Calcined Hot Ore, The Charging of, 
328. 

Calcined Ore, Analysis of, 175. 

Calcined Ore, The Calculation of 
Matte from, 175. 

Calciners, Curtain Arch for, 167. 

Calciners, Reverberatory, 146. 

Calciners with Open Hearth, Rever¬ 
beratory, 146. 

Calcining Furnace, the Capacity of, 
177. 

Calcining Furnaces, 133. 

Calcining in Bruckner’s Cylinders, 
Cost of, 140. 

Calcining in the Spence Furnace, 
Cost of, 143. 

Calcining, Results obtained in Spence 
Furnace, 143. 

Calcining, Shaft Furnaces for, 133. 

Calcining, The Chemistry of, 168. 

Calcining, Use of Revolving Cylinders 
for, 135. 

Calumet & Heela Mine, Description 
of, 12. 

Calumet & Heela Mine, The Produc¬ 
tion of, 10. 

Canadian Copper Co.’s Method of 
“ V-Roasting,” 86. 

Capacity of Butte Furnace, 204. 

Capacity of Calcining Furnaces, 177. 

Capacity of Crushing Plant, The, 
133. 

Capacity of Furnace Affected by Blast 
Pressure, 257. 

Capacity of Furnace Lessened by 
Fines, 281. 

Capacity of Herreshoff Furnace, 204. 

Capacity of Manhes’ Converters, 382. 

Capacity of Phoenixville Furnace, 
204. 

Capacity of Reverberatory Furnaces, 
304. 

Capacity of Roast-stalls, The, 96. 

Capacity of Strafford Furnace, 204. 

Carbonate Mines of Arizona, The, 19. 

Cement, Amount Required in Building 
a Reverberatory, 314. 

Cement Copper Produced by Hunt & 
Douglas Method, 347. 

Cement Copper Refined at Atvida- 
berg, 363. 

Cement Copper, The Treatment of, in 
Blister Furnace, 347. 

Cement, Hydraulic, Used in Bricking 
Ore Fines, 278. 

Chain Elevators, 132. 

Chalcocite, 4. 

Chalcocite, Analysis of, 5. 

Chalcopyrite, 3. 

Chalcopyrite at Capelton, P. Q., 8. 


Chalcopyrite at Ely, Vt., 8. 

Chalcopyrite in Newfoundland, 8. 

Chalcopyrite, Oxidation of at Sur¬ 
face, 8. 

Charcoal, The Use of in Calcination, 
172. 

Charcoal, Use of in Smelting Nickel 
Ores, 294. 

Charge for Refinery, The Size of, 345. 

Charge for Reverberatories, Increase 
in Weight of, 325. 

Charge for Reverberatories, The Size 
of, 323. 

Charge, The Size of, for Cupolas, 259. 

Charge, The Size of, for Herreshoff 
Furnace, 204. 

Charging-door for Cupola, 206. 

Charging Reverberatories, 322. 

Chemistry, The, of the Calcining Pro¬ 
cess, 168. 

Chili, The Grade of Matte from Cre- 
smelting in, 320. 

Chilian Mills, 128. 

Chilled Iron Shells for Cornish Rolls, 
130. 

Chills from Forehearth, Analysis of, 

200 . 

Chimney Lining, Air-space in, 330. 

Chimney, Proper Size of, for Roast- 
stalls, 100. 

Chimneys for Roast-heaps, 70. 

Church, Prof. J. A., Bricking Fines 
with Clay, 280. 

Classification of Crushed Ore for 
Heap-roasting, 49. 

Clay, Amount Required in Building a 
Reverberatory, 314. 

Clay, The Addition of, in Bricking 
Ore Fines, 278. 

Clifton District, A. T., The, 20. 

Clifton Furnace, Description of, 214. 

Clifton Slag, Analysis of, 215. 

Clinker Grate, The Economy of, 310. 

Coarse Metal, Ore-smelting for, 319. 

Coarse Metal, Richness of, 320. 

Coke, Amount of used in Smelting 
Nickel Ores, 294. 

Coke, Per cent, of Ash in, 220. 

Colorado, The Copper Production of, 
18. 

Colorimetric Determination of Cop¬ 
per, 37. 

Comparative Results of Smelting, 

220 . 

Concentration of Matte by Oxidizing 
Fusion, 335. 

Conglomerate Mines, The, 9. 

Construction of Reverberatory Cal¬ 
ciners, 150. 

Converter Linings, 382. 




INDEX. 


387 


Converter, Manhes’, The Position of 
the Tuyeres in, 381. 

Converters, Capacity of, 383. 

Converters, Loss of Silver in, 383. 

Converters, The Appearance of the 
Flame from, 382. 

Converters, The Necessity of Two 
Sets of, 381. 

Converters, The Production of, at the 
Parrot Works, 383. 

Converters, The Value of Slag from, 
for Flux, 383. 

Cooling of Reverberatory Hearth, 309. 

Copper, Absorption of, by Refining 
Furnace Bottom, 344. 

Copper, Arizona, Purity of, 220. 

Copper-assaying, 29. 

Copper, Bad Method of Grading, in 
the U. S., 375. 

Copper, Best-selected, The Manufact¬ 
ure of, 379. 

Copper, Blister, Analysis of, 338. 

Copper, Blister, The Making of, 335. 

Copper, Blister, The Refining of, at 
Atvidaberg, 370. 

Copper, Color of, 349. 

Copper, Color of Affected by Cool¬ 
ing Water, 349. 

Copper, Easily Detected by Prospect¬ 
ors, 26. 

Copper, Future of, in the U. S., 22. 

Copper, Inferior, has its Uses, 377. 

Copper, Lake Superior, The Purity 
of, 343. 

Copper, Loss of, by Leaching, 107. 

Copper Mattes, The Bessemerizing of, 
380. 

Copper, Metallic, The Desulphuriza¬ 
tion of, 289. 

Copper, Methods of Assaying of, 33. 

Copper Ores Carrying Au and Ag, 
The Treatment of, 378. 

Copper, Oxidation of in Refining, 
369. 

Copper Purchases at Swansea, 183. 

Copper, Quality of, Judged Mainly by 
its Color in the U. S., 376. 

Copper Queen Furnace, Amount of 
Water used in, 210. 

Copper Queen Furnace, Forehearth 
of, 219. 

Copper Queen, Matte-roasting at, 221. 

Copper Queen Mine, The, 21. 

Copper Queen Mine, The Average of 
its Ore, 22. 

Copper Queen Slag, Analysis of, 214. 

Copper Queen Smelter, 209. 

Copper, Refined, Color of, 349. 

Copper, Refined, Method of Direct 
Casting, 359. 


Copper Refining, 343. 

Copper Refining, The Cost of, 360. 

Copper Refining, The Period of Pol¬ 
ing, 356. 

Copper Refining with Gas at Atvida- 

j berg, 363. 

I Copper Smelting, Subdivisions of, 
182. 

Copper, The Removal of Antimony 
from, 356. 

Copper, The Removal of Arsenic 
from, 356. 

Copper, The Sampling of, 30. 

Copper, The Smelting of, 181. 

Copperas, Use of, in Bricking Ore 
Fines, 278. 

Cornish Rolls, 129. 

Cornish Rolls, Breaking-cups for, 132. 

Cornish Rolls, Capacity of, 133. 

Cornish Rolls, Chilled Iron Shells for, 
130. 

Cornish Rolls, Proper Speed of, 132. 

Cornish Rolls, Shells for, 130. 

Cornish Rolls, Springs for, 131. 

Cornish Rolls, Steel Shells for, 130. 

Cost of Breaking Ore by Hand, 55. 

Cost of Brick Blast-furnaces, Esti¬ 
mate of, 251. 

Cost of Bricking Ore Fines, 279. 

Cost of Calcining in Bruckner’s Cyl¬ 
inders, 140. 

Cost of Calcining in the Spence Fur¬ 
nace, The, 143. 

Cost of Cupola Smelting, 253. 

Cost of Heap-roasting, 83. 

Cost of Reverberatory Calciners, 165. 

Cost of Roast Stalls, 109. 

Cost of Smelting in Herreshoff Fur¬ 
nace, 204. 

Cost of Smelting in Large, Brick Fur¬ 
naces, 254. 

Cost of Stall-roasting, 109. 

Crushing Machinery, 126. 

Crushing Ore by Hand, 48. 

Crushing Ore by Machinery, 48. 

Crushing Ore, The Cost of, 50. 

Crushing Plant for Heap-roasting, 
50. 

! Cupola for Melting Matte for Con¬ 
verters, 382. 

Cupola Smelting, Cost of, 253. 

Cupola Smelting, Resume of Results 
of, by Howe, 285. 

Cuprite, 1. 

Curtain Arch for Calciners, 167. 

I Cyanide Assay, 33. 

Cyanide Assay, Torrey & Eaton’s 
Investigations upon the, 36. 

Cylinders, Revolving, The Use of for 
Calcination, 135. 






388 


INDEX. 


D 

Decrepitation of Ore during Calcina¬ 
tion, 124. 

Desulphurization, Degree of, during 
Heap-roasting, 84. 

Detroit Refining Works, Stacks at, 
164. 

Detroit Works at Clifton, Furnace at, 
214. 

Dimensions of Matte Stalls, 116. 

Dinas Brick, Use of, in Reverberatory 
Arches, 302. 

Douglas, Janies, Inventor of Hunt & 
Douglas Method, 347. 

Douglas, James, Paper by, on Copper 
Resources of the U. S., 20. 

Drainage of Roast-yard, 63. 

Drying Reverberatory Furnaces, 305. 

Dryness Essential to Roast-yard, 292. 

Dry-sweating of Copper after Vivian, 
354. 

Ducktown, Tenn., Copper Mines of, 
23. 

Dump at Smelter, Importance of 
Keeping, Level, 264. 

E 

Economy of Clinker Grate, 310. 

Egleston’s Observations on Oxygen 
in Copper, 356. 

Egleston’s, T., Paper on the Manlies 
Process, 380. 

Electrolytic Assay of Copper, 38. 

Electrolytic Assay of Copper, Torrey 
& Eaton’s Investigations on, 38. 

Electrolytic Assay of Nickel, 43. 

Electrolytic Precipitation of Nickel, 
296. 

Elevators for Fine Ore, 132. 

Ely Method of Making Black Copper, 
288. 

Ely Mine, Vt., 23. 

Ely Ore, Results of Heap-roasting, 

84. 

Ely Pig-copper, Analysis of, 273. 

Enlargement of Reverberatory Fur¬ 
naces, 324. 

Erubescite, 5. 

Eustis, W. E. C., Observations on 
Addition of Lime to Calcined Matte, 
278. 

Evil of Basic Charges in Reverbera¬ 
tory Smelting, 321. 

Excavation for Foundation of Roast 
Stalls, 110. 

Excavation for Reverberatory Foun¬ 
dations, 300. 

Expense per Ton for Crushing Ore, 

51. 


Experiments in Bessemerizing Matte 
at Orford Works, 334. 

Explosions of Slag, 264. 

F 

Fan-blowers, 265. 

Feed-pipes for Water-jacket, 287. 

Fettling, Best Material for, 311. 

Fettling Reverberatory Furnace, 310. 

Fine Grinding of Ore Essential for 
Bricking, 280. 

Fine Ore, Agglomeration of, 276. 

Fine Ore Bricked with Clay, 280. 

Fine Ore, Cost of Bricking, 279. 

Fine Ore, Effect of, on Smelting, 261. 

Fine Ore, Krause’s Method of Ag¬ 
glomerating, 280. 

Fine Ore, Reduction of Capacity of 
Furnace by, 281. 

Fine Ore, Treatment of in Blast-fur¬ 
nace, 275. 

Fines, Green, Results of Smelting, 
284. 

Fines, Production of in Crushing, 48. 

Fire-clay Needed in Building Rever¬ 
beratory, 313. 

Firing Roast Stalls, 102. 

Flame from Converter, Appearance 
of, 382. 

Flapping Copper during Refining, 
371. 

Floods, Loss of Ore by, 66. 

Flue of Reverberatory, 302. 

Flux, Barren, Use of in Matte Smelt¬ 
ing, 271. 

Flux, Value of Converter Slags for, 
382. 

Fore-liearth at Copper Queen, 219. 

Fore-hearth, Improved Wrought-iron, 
287. 

Fore-liearth of Lake Superior Slag 
Cupola, 219. 

Fore-hearths, Analysis of Chills from, 

200 . 

Fore-hearths, Asbestos Packing for, 

201 . 

Fore-heartlis, Brick, 198. 

Foundation of Stacks, 159. 

Foundations of Reverberatory Fur¬ 
nace, 300. 

Foundations of Roast Stalls, 110. 

Fournet’s Law of Affinities, 181. 

Fraser & Chalmers’ Water-jacket, Cut 
of, 224. 

Fuel Best Suited to Copper Refining, 
344. 

Fuel Consumption at Atvidaberg, 368. 

Furnace, Water-jacket, 186. 

Furnace, Water-jacket, Amount of 
Water Required for, 188. 




INDEX. 


389 


Furnace, Water-jacket, Tlie Form of, 
187. 

Fusion of Unroasted Matte, 272. 

Future of Copper in the U. S., 22. 

G 

Gas, Refining Copper with, in 
Sweden, 363. 

General Remarks on Blast-furnaces, 
256. 

Geology of the Ontario Nickel Dis¬ 
trict, 290. 

Gerstenhofer Furnace, 134. 

Gestuebbe (Steep), Manufacture of, 
193. 

Gilchrist’s Method of Refining Copper, 

3 / 4. 

Gilchrist’s, Percy A., Paper on Basic- 
lined Furnaces, 339. 

•Gilchrist’s Table of Results of Treat¬ 
ment of White Metal on the Basic 
Hearth, 341. 

Gilpin County, Colorado, Mines in, 17. 

Gilpin County'' Mines, Per cent, of 
Copper in, 17. 

Glenn, Win., Paper by, on Heap- 
roasting, 70. 

Globe Smelter, 209. 

Gold- and Silver-bearing Ores, The 
Treatment of, 378. 

Grant Smelting Works, Improvement 
in Matte-tapping at, 270. 

Granulation of Matte, 125. 

Granulation of Slag by Water, 288. 

Grate, Clinker, Economy of, 311. 

Green Fines added to Smelter at Sud¬ 
bury, 293. 

Green Fines, Agglomerating with 
Slag, 280. 

Green Fines, Results of Smelting at 
Orford, 284. 

Green Fines, Smelting of, 282. 

Green Fines, Thomson’s Method of 
Smelting, 283. 

Griffith, Analysis of Ore Knob Copper 
by, 274. 

Grinding Fine Necessary for Bricking 
Ore, 280. 

Gutters for Slag, 325. 

H 

Hammers for Ore-spalling, 52. 

Hammond-Spence Furnace, Im¬ 
proved, 144. 

Hand-breaking of Ore, The, 52. 

Hand-breaking Ore, The Cost of, 55. 

Heap-roasting, Analysis of Matte 
from, 79. 

Heap-roasting, Appearance of Prod¬ 
uct of, 85. 


Heap-roasting at Butte a Serious Evil 
59. 


Heap-roasting, Building 
89. 


of Heap in 


J 




Heap-roasting, Cost of, 91. 
Heap-roasting, Damage Caused by, 
57. 


Heap-roasting, Degree of Desulphuri¬ 
zation, 84. 

Heap-roasting, Elevated R. R. for, 64. 
Heap-roasting, Estimates of Cost of, 
83. 


Heap-roasting, Illustration of Yard 
for, 65. 

Heap-roasting, Importance of 
Thorough Drainage, 63. 

Heap-roasting, Length of Time Re¬ 
quired for, 68. 

Heap-roasting, Loss of Ore by 
Floods, 66. 

Heap-roasting, Means for Obviating 
Damage from, 58. 

Heap-roasting of Copper Ores, 56. 

Heap-roasting of Matte, 88. 

Heap-roasting of Nickel Ores in On¬ 
tario, 292. 

Heap-roasting often Badly Executed, 
56. 


Heap-roasting, Preparation of Ground 
for, 61. 

Heap-roasting, Production of Matte 
in, 78. 

Heap-roasting, Size of Heaps in, 
67. 

Heap-roasting, Size of Roast-yard in, 
62. 


Heap-roasting, Sulphur Obtained in, 
75. 

Heap-roasting, Table of Results of, 
80. 


Heap-roasting, Turn-table for, 66. 

Hearth Furnace, Automatic, for Cal¬ 
cining, 141. 

Hearth, Reverberatory, Cost of Mak¬ 
ing, 317. 

Hearth. Reverberatory, Floated up by 
Chunks of Iron, 310. 

Hearth, Reverberatory, Increase in 
Size of, 324. 

Hearth, Reverberatory, Method of 
Making, 306. 

Hearth, Reverberatory, Smelting-in 
of, 308. 

Hearth Sand, Analysis of, 306. 

Heated Blast for Copper Smelting, 
258. 


Height of Stack for Reverberatories, 
305. 


Height of Stacks, 161. 

Height of Water-jackets, 206. 





390 


INDEX. 


Henrich’s, C., Description of Clifton 
Furnace, 214. 

Herreshoff Furnace, 195. 

Herreshoff Furnace, Capacity of, 204. 

Herreshoff Furnace, Cost of Smelting 
in, 204. 

Herreslioff Furnace, Size of Charge 
for, 204. 

Herreshoff Furnace, Wendt’s De¬ 
scription of, 200. 

Herreshoff’s Late Improvements in 
Blast-furnaces, 286. 

Horse-power Required by Blowers, 
268. 

Hot Calcined Ore, Use of, 328. 

Howe, H. M., Experiments on Fans 
by, 267. 

Howe’s, Id. M., Resume of Cupola 
Smelting, 285. 

Hunt & Douglas Method, 347. 

Hunt & Douglas Method Applied to 
Gold and Silver Mattes, 378. 

Hydrochloric Acid, Effect of, on Cya¬ 
nide Assay, 37. 

I 

Improvements in Blast-furnaces, 
Late, 286. 

Iron Used for Floating Furnace Bot¬ 
toms, 310. 

Iron Work of New, Large Reverbera- 
tories, 332. 

Iron Work of Reverberatories, 314. 

Ironing of Reverberatory Furnaces, 
303. 

Ironing of Stacks, 163. 

Irregularities in Orford Furnace, 237. 

J 

Jaw-crushers, 127. 

Jaw-crushers, Multiple, 128. 

Johnson, Paul, Description by, of 
Gas-refining in Sweden, 363. 

K 

Kernel-roasting, 85. 

Keweenaw Rocks of Lake Superior, 
27. 


Labor Required for New, Large Re¬ 
verberatory, 331. 

Labor Used in Building Reverbera¬ 
tory, 312. 

Ladles Used in Refining, 359. 

Ladling Refined Copper at Atvida- 
berg, 373. 

Lake Superior Copper, Purity of, 343. 
Lake Superior Deposits, 9. 

Lake Superior Deposits, Future Prom¬ 
ise of, 27. 

Lake Superior Slag Cupola, 216. 

Lake Superior Slag Cupola, Fore- 
hearth of, 219. 

Late Improvements in Blast-fur¬ 
naces, 286. 

Lead, Effect of, on Cyanide Assav, 

36. 

Lead, Effect of, on Electrolytic Assay,. 
38. 

Length of Reverberatory Calciners, 
148. 

Life of Water-jackets, 222. 

Lime, Effect of, on Cyanide Assav, 

37. 

Lime, Importance of, in Reducing 
CuS, 278. 

Lime Mortar Unfit to Stand Heat, 
98. 

Lime, Proportion of, Necessary for 
Bricking Ore, 277. 

Lime Required to Build Reverbera¬ 
tory, 314. 

Lime, Use of, for Bricking Fine Ore,. 
276. 

Lining of Manlies Converter, 382. 
Loss of Copper by Leaching, 107. 
Loss of Ore by Floods, 66. 

Loss of Silver in Bessemerizing, 383. 
Lumber Required to Build Rever¬ 
beratory, 316. 

Lump Ores, Difficulty of Sampling, 
32. 

Lump Ores Roasted in Kilns, 118. 
Luting Furnace Doors with Slimes, 
321. 

M 


Kilns, Description of, 118. 

Kilns for Matte at Copper Queen, 
Management of, 121. 

Kilns, The Roasting of Ores in, 118. 
Kilns, Used Mostly in Making Sul¬ 
phuric Acid, 118. 

Kindling Roast-heaps, 72. 

Krause, O. K., Method of Agglomer¬ 
ating Fine Ore, 280. 

L 

Labor in Building Roast-heaps, 111. 


Machinery for Crushing Ore and 
Matte, 126. 

Machinery for Final Pulverization, 
128. 

Machinery for Preparatory Crushing, 
126. 

Magnesia, Effect of, on Cyanide As¬ 
say, 37. 

Maine Pyrites Mines, 23. 

Making Blister Copper, 335. 

Making Blister Copper, The Time Re¬ 
quired for, 336. 








INDEX. 


391 


Making Blister Copper, The Weight 
of Charge in, 335. 

Malachite, 3. 

Management of Matte Stalls, 115. 

Management of Reverberatories, 309. 

Management of Roast-heaps, 73. 

Management of Water-jacket Fur¬ 
naces, 211. 

Manganic Sulphide, The Calcination 
of, 171. 

Manhes Converter, Position of Tuy¬ 
eres in, 381. 

Manhes, P., Inventor of Successful 
Bessemerizing, 380. 

Manhes, P., Plant at the Parrot 
Works, 380. 

Manhes Process, The Size of Charge 
in, 380. 

Manufacture of Slag-brick, 93. 

Mary Ore, Loss in Roasting, 108. 

Mason Work on Roast Stalls, Cost 
of, 111. 

Material, Estimate of, for Building 
Reverberatories, 312. 

Material, Estimate of, for New, Large 
Reverberatories, 331. 

Matte, Analysis of, 79. 

Matte, Breaking-out of, in Brick Fur¬ 
naces, 236. 

Matte, Building Roast-heap of, 89. 

Matte, Calcination of Pulverized, 123. 

Matte, Calculation of Production of, 
175. 

Matte Enriched by Oxidizing Smelt¬ 
ing, 288. 

Matte, Experiments on Bessemeriz¬ 
ing, 334. 

Matte, Fusion Assay of, 174. 

Matte, Granulation of, in Water, 125. 

Matte, Heap-roasting of, 88. 

Matte, Improvements in Tapping of, 
at The Grant Smelting Works, 270. 

Matte, Nickel, its Peculiarities, 294. 

Matte, Nickel, Treatment of, 295. 

Matte, Nickel, Use of Steep in Smelt¬ 
ing, 295. 

Matte, Parrot Co.’s Assays of, 320. 

Matte, Pouring of, on Plates to Cool, 

270. 

Matte, Production of, in Heap-roast¬ 
ing, 78. 

Matte-roasting at Copper Queen, 221. 

Matte-roasting, Cost of, 91. 

Matte, Roasting of, in Ore Stalls, 114. 

Matte Smelting in Blast-furnaces, 

271. 

Matte, Stall-roasting of, 115. 

Matte Stalls, Dimensions of, 116. 

Matte Stalls, Management of, 115. 

Matte Stalls, Results of, 117. 


Matte, Table of Concentration of, 
335. 

Matte to be Tapped Seldom in Rever¬ 
beratories, 330. 

Matte, Treatment of, 80. 

Matte, Unroasted, The Fusion of, 272. 

Mattes, Copper, The Bessemerizing 
of, 380. 

Mattes, The Bessemerizing of, Loss 
of Silver during, 382. 

McArthur. James, Inventor of “V- 
Method ” of Roasting, 87. 

Mechanical Condition of Ore for 
Smelting, 275. 

Melaconite, 2. 

Metal, Coarse, Ore-smelting for, 319. 

Metal, Coarse, Richness of, 320. 

Metallic Bottoms, Analysis of, 340. 

Metallic Bottoms, Concentration of 
As in, 340. 

Metallic Bottoms, Gilchrist’s Treat¬ 
ment of, 340. 

Metallic Bottoms, Results of Treat¬ 
ment of, 341. 

Metallic Copper Resulphurized, 289. 

Methods of Copper Assaying, 29, 33. 

Method of Direct Casting of Refined 
Copper, 359. 

Miscellaneous Expenses in Building 
Roast Stalls, 114. 

Miscellaneous Materials for Large 
Reverberatories, 333. 

Modern Blast-furnace Apparatus, 269. 

Moisture, The Determination of, 32. 

Molds for Slag-brick, 94. 

Molds used in Copper Refining, 359. 

Moose Mine, Experiments at, in 
Smelting Fine Ore, 281. 

Mountain System of Veins, 15. 

Muffle Calciner, The, 166. 

Multiple Jaw-crushers, 128. 

Murphy, D. P., Assays Made by, 320. 

N 

Nacimiento Mines, N. M., 20. 

Native Copper, 1. 

Nevada County, Cal., Mines, 20. 

New, Large Reverberatories, Esti¬ 
mate of Cost of, 331. 

Nickel, Determination of, by Battery 
Assay, 43. 

Nickel District, The Geology of the, 
290. 

Nickel, Effect of, on Electrolytic As¬ 
say, 39. 

Nickel, Electrolytic Precipitation of, 
297. 

Nickel in Ontario, 290. 

Nickel in Pyritous Ores, The Smelt¬ 
ing of, 290. 






392 


INDEX. 


Nickel Matte, Bessemerizing of, 296. 

Nickel Matte, its Peculiarities, 294. 

Nickel Matte, The Treatment of, 295. 

Nickel Matte, The Use of Steep in 
Smelting, 295. 

Nickel, Metallic, Fine Display of, by 
Wharton, 298. 

Nickel Ores, The Amount of Coke 
used in Smelting, 294. 

Nickel Ores, The Use of Charcoal in 
Smelting, 294. 

Nickel, The Refining of, 297. 

Nickel, The Treatment of, by Vivian 
& Co., 297. 

Nickeliferous Pyrrhotite, The Roast¬ 
ing of, 291. 

Nolten, Analysis of Ely Pig Copper 
by, 273. 

O 

O’Hara’s Mechanical Calciner, 141. 

Ontario, The Occurrence of Nickel in, 
290. 

Open Roast Stalls, 92. 

Orange Mts., N. J., Occurrence of 
Ckalcocite in, 5. 

Ore-breaking by Hand, 52. 

Ore-breaking by Hand, The Cost of, 
55. 

Ore, Calcination of Pulverized, 123. 

Ore Fines, Treatment of, in Blast-fur¬ 
nace, 275. 

Ore Knob Mine, N. C., Mine of, 23. 

Ore Knob Pig Copper, Analysis of, 
274. 

Ore Knob Refinery, The Use of Wood 
at, 345. 

Ore Roast Stalls, 96. 

Ore, Size to Crush to for Calcining, 
123. 

Ore Slimes, The Use of, for Lute, 321. 

Ore Smelting for Coarse Metal, 319. 

Ores of Copper, The Description of, 1. 

Ores of Copper, The Distribution of, 7. 

Ores Suited to Blast-furnaces, 185. 

Ores, Sulphide, The Treatment of, 
184. 

Ores, The Roasting of, in Lump 
Form, 45. 

Orford Co.’s Experiments on Smelting 
Green Fines, 283. 

Orford Co.’s Matte from Green Fines, 
284. 

Orford Co.’s Results in Smelting 
Green Fines, 284. 

Orford Furnace, 227. 

Orford Furnace, Addition of Silica to 
Charge, 239. 

Orford Furnace Bottom, The Con¬ 
struction of, 232. 


Orford Furnace, Change of Shape by 
Burning out, 242. 

Orford Furnace, Cost of Smelting in, 
254. 

Orford Furnace, Irregularities likely 
to Occur in, 237. 

Orford Furnace, Number of Tuyeres 
in, 229. 

Orford Furnace, Siphon Tap of, 233. 

Orford Furnace, The Use of Fan- 
blowers with, 267. 

Orford Works, Experiments at, on 
Bessemerizing Mattes, 334. 

Oscura Copper Mines, N. M., 20. 

Oxidation of Copper during Refining, 
The, 369. 

Oxidation of Copper Ores in Depth,. 
24. 

Oxidation while a Furnace is Banked, 
247. 

Oxide of Iron, The Effect of, on the 
Cyanide Assay, 35. 

Oxidized Ore-smelting in Cupolas, 
208. 

Oxidizing Fusion of Matte, Table of 
Results, 335. 

Oxidizing Roasting, 46. 

Oxidizing Smelting to Enrich Matte, 
288. 

Oxygen Present in Copper, 356. 

P 

Parke Automatic Calciner, 146. 

Parrot Co.’s Matte, Assays of, 320. 

Parrot S. & C. Co., Roast Stalls at, 93. 

Parrot S'. & C. Co., Use of Spence 
Furnace by, 143. 

Parrot Works, The Manlies Plant at, 
380. 

Parrot Works, The Production of the 
Bessemerizing Plant at, 383. 

Patent Pulverizers, 128. 

Pearce, R., Improvements by, in 
Reverberatory Smelting, 324. 

Pearce, R., Method of Covering 
Roast Stalls, 101. 

Peculiarities of Nickel Matte, 294. 

Percy, Analysis of Atvidaberg Pig 
Copper, 274. 

Percy, Analysis of Hearth Sand, 306. 

Permian Formation in N. M., 20. 

Peters, E. D., Jr., Analysis of Ely Pig 
Copper, 273. 

Phillips Ore, The Result of Heap- 
roasting, 84. 

Plioenixville Furnace, The Capacity 
of, 204. 

Pimple Metal Treated on Basic 
Hearth, 342. 

Pipe, Blast, The Construction of, 268. 




INDEX. 


393 


Pique Mine, Cliili, The, 17. 

Plates for Cooling Matte on, 270. 

Plattner’s Work on Roasting, 46. 

Poling of Blister Copper at Atvida- 
berg, 372. 

Poling of Copper, The, 356. 

Powder, Use of, in Tearing Down 
Roast-heaps, 82. 

Power Required by Blowers, The, 
268. 

Precipitation of Copper with Zinc, 37. 

Preparatory Crushing, The Machines 
for, 126. 

Pressure in Agglomerating Fine Ore, 
276. 

Pressure of Blast Affecting Smelting 
Rate, 257. 

Production of the Bessemerizing 
Plant at Parrot Works, 383. 

Pulverization, The Machines for, 128. 

Pulverized Material, The Difficulties 
in Calcining, 123. 

Pulverized Ore, The Calcination of, 
123. 

Purity of Arizona Copper, The, 220. 

Pyrites, The Roasting of, in Kilns, 

121 . 

Pyrites Used in Acid-making, 119. 

Pvritous Ores of Copper and Nickel, 
The Smelting of, 290. 

Pyrrhotite Containing Nickel in On¬ 
tario, 290. 

Pyrrhotite, Ontario, its Geology, 290. 

Pyrrhotite used instead of Pyrite, 120. 

Q 

Quartering Shovel of Brunton’s for 
Sampling, 32. 

Quartz for Fettling, 310. 

Quincy Mine, 11. 

R 

Rapid Smelting, The Secret of, 321. 

Ray Mine, The Description of, 13. 

Reducing Roasting, The, 46. 

Refining Blister at Atvidaberg, Size 
of Charge in, 370. 

Refining Blister Copper at Atvida¬ 
berg, 370. 

Refining Furnace, Description of, 344. 

Refining Furnace, Importance of 
Sound Bottoms, 344. 

Refining of Copper, 343. 

Refining of Copper, Color of Product, 
349. 

Refining of Copper, Cost of, 360. 

Refining of Copper, Description of, 
347. 

Refining of Copper, Details of the, 


Refining of Copper, Fuel Best Suited 
to, 344. 

Refining of Copper in Basic-lined 
Furnaces, 374. 

Refining of Copper, Ladles used for, 
359. 

Refining of Copper, Method of Direct 
Casting, 359. 

Refining of Copper, Molds used in, 359. 

Refining of Copper, Period of Poling, 
356. 

Refining of Copper, Size of Charge in, 
345. 

Refining of Copper, Vivian’s Dry¬ 
sweating Process, 354. 

Refining of Copper with Gas at At¬ 
vidaberg, 363. 

Refining of Copper, Wood Advanta¬ 
geous, 345. 

Refining of Nickel, The, 297. 

Repairs on Brick Blast-furnaces, 248. 

Resulphurization, The, of Metallic 
Copper, 289. 

Results of Stall-roasting, 105. 

Resume of Cupola Smelting by Howe, 
285. 

Reverberatory, Analysis of Hearth 
Sand, 306. 

Reverberatory, Arch of, 302. 

Reverberatory Calciners, 146. 

Reverberatory Calciners, Buckstaves 
for, 155. 

Reverberatory Calciners, Building 
for, 165. 

Reverberatory Calciners, Construc¬ 
tion of, 150. 

Reverberatory Calciners, Construc¬ 
tion of Arch of, 153. 

Reverberatory Calciners, Construc¬ 
tion of Stack, 159. 

Reverberatory Calciners, Cost of Con- 

• struction of, 155. 

Reverberatory Calciners, Drying of, 

157. 

Reverberatory Calciners, Length of, 
148. 

Reverberatory Calciners, Repairs on, 

i66. 

Reverberatory Calciners, Slating 
Arch of, 157. 

Reverberatory Calciners, Tie-rods for, 
155. 

Reverberatory Calciners, Tools for, 

158. 

Reverberatory Calciners, Width of, 
146. 

Reverberatory Calciners with Closed 
Ash-pits, 152. 

Reverberatory Calciners with Open 
Hearth, 146. 









394 


INDEX. 


Reverberatory Calciners, Working 
Doors of, 149. 

Reverberatory, Capacity of, 304. 

Reverberatory, Charging, 322. 

Reverberatory, Cooling of Hearth, 
309. 

Reverberatory, Drying of, 306. 

Reverberatory, Enlargement of, 324. 

Reverberatory, Estimate of Brick 
Work, 313. 

Reverberatory, Estimate of Cement, 
314. 

Reverberatory, Estimate of Clay, 
etc., 314. 

Reverberatory, Estimate of Cost of 
Bottoms, 317. 

Reverberatory, Estimate of Cost of 
Large Modern, 331. 

Reverberatory, Estimate of Cost of 
Running, 317. 

Reverberatory, Estimate of Fire-clay, 
314. 

Reverberatory, Estimate of Iron 
Work, 314/ 

Reverberatory, Estimate of Labor 
and Material on, 312. 

Reverberatory, Estimate of Lime, 
314. 

Reverberatory, Estimate of Lumber, 
316. 

Reverberatory, Estimate of Sand, 
314. 

Reverberatory, Estimate of Stone 
Work, 313. 

Reverberatory, Estimate of Wrought- 
iron, 315. 

Reverberatory, Evil of Basic Charges, 
321. 

Reverberatory, Excavation for, 312. 

Reverberatory, Excavation for Foun¬ 
dation of, 300. 

Reverberatory, Fettling of, 310. 

Reverberatory Furnaces, 299. 

Reverberatory Furnaces, Processes 
Executed in, 299. 

Reverberatory, Granulation of Slag 
from, 325. 

Reverberatory, Height of Stack of, 
305. 

Reverberatory, Increase in Weight of 
Charge, 325. 

Reverberatory, Ironing of a, 303. 

Reverberatory, Large, Cost of Brick 
Work, 331. 

Reverberatory, Large, Cost of Iron 
Work, 332/ 

Reverberatory, Large, Labor on, 333. 

Reverberatory, Large, Resume of 
Totals, 333. 

Reverberatory, Management of, 309. 


Reverberatory, Method of Making 
Hearth, 306. 

Reverberatory, Miscellaneous Mate¬ 
rial, 333. 

Reverberatory, Necessity of Air-space 
in Stack Lining, 330. 

Reverberatory, Pre-heating of Air 
for, 325. 

Reverberatory, Size and Shape of 
Flue, 302. 

Reverberatory, Size of Charge for, 
323. 

Reverberatory Slag-gutters, 325. 

Reverberatory Smelting, Advances 
Made at Anaconda in, 324. 

Reverberatory Smelting, Advances 
Made by R. Pearce in, 324. 

Reverberatory Smelting, Advantages 
of Two Skimming-doors, 330. 

Reverberatory Smelting, English 

Wheelbarrow System, 329. 

Reverberatory Smelting, Improve¬ 
ments in, 324. 

Reverberatory Smelting, Matte to be 
Tapped Seldom, 330. 

Reverberatory Smelting, Various 
Economies, 329. 

Reverberatory, The Smelting-in of 
Hearth, 308. 

Reverberatory, Summary of Totals, 
316. 

Reverberatory, Table of Results, 312. 

Reverberatory, Tapping, 322. 

Reverberatory, Tools Required for,. 
316. 

Reverberatory, Use of Hot Ore in, 
328. 

Revolving Cylinder for Calcining, 
135. 

Richard’s, Prof. R. H., Tuyere Joint, 
205. 

Richness of Coarse Metal from Ore 
Smelting, 320. 

Rio Tinto Pyrites, Analysis of, 119. 

Roast Stalls, Capacity of, 96. 

Roast Stalls, Cost of Tracks, 112. 

Roast Stalls, Excavation for Founda¬ 
tions of, 110. 

Roast Stalls for Ore, 96. 

Roast Stalls, Labor in Building, 111. 

Roast Stalls, Mason Work on, 111. 

Roast Stalls, Miscellaneous Expenses 
of, 114. 

Roast-heaps, Building of, 69. 

Roast-heaps, Chimneys for, 70. 

Roast-heaps, Kindling, 72. 

Roast-heaps, Management of, 73. 

Roast-heaps should not be disturbed 
till burnt out, 77. 

Roast-heaps, Stripping of, 78. 



INDEX. 


395 


Roast-heaps, Tearing Down of, 81. 

Roast-heaps, Use of Powder in, 82. 

Roasting in Stalls, Advantages of, 
106. ’ 

Roasting in Stalls, Cost of, 109. 

Roasting in Stalls, Cost of Stalls, 109. 

Roasting in Stalls, Elimination of As 
and Sb, 104. 

Roasting in Stalls, Removal of Ore, 
104. 

Roasting in Stalls, Results of, 105. 

Roasting in Stalls, Time Required, 
103. 

Roasting Lump Ores in Kilns, 118. 

Roasting Nickel Ores, Proper Size of 
Ore for, 293. 

Roasting Nickeliferous Pyrrhotite in 
Ontario, 291. 

Roasting of Copper Ores in Lump 
Form, The, 45. 

Roasting of Matte at Copper Queen, 

221 . 

Roasting of Matte in Stalls, 115. 

Roasting Ore in Heaps, 56. 

Rolls, Cornish, 129. 

Rolls, Cornish, Shells for, 130. 

S 

Salamanders, Avoidance of, 190. 

Sampling, Importance of, 29. 

Sampling, Quartering Shovel for, 32. 

Sampling-machine, Automatic, 30. 

San Juan, Col., Mines, 18. 

Sand Hearth, Analysis of, 306. 

Sand Required for Reverberatory, 
Estimate of, 315. 

Santa Rita Mines, 14. 

Screen for Sizing Ore, 49. 

Shaft Furnaces for Calcining, 133. 

Shape of Furnace during Campaign, 
Change in, 242. 

Shells for Cornish Rolls, 130. 

Shells for Rolls, Turning Surface of 
Smooth*, 131. 

Silica, Addition of, to Over-hot Fur¬ 
nace, 239. 

Silica, Amount of, in Slag, 185. 

Silica, High per cent, of, in Slag, 283. 

Silica of Soda for Bricking Fines, 276. 

Silver- and Gold-bearing Copper Ores, 
The Treatment of, 378. 

Silver, Effect of, on Cyanide Assay, 
36. 

Silver, Effect of, on Electrolytic As¬ 
say, 38. 

Silver in Butte Ores, 16. 

Silver, Loss of, in Bessemerizing 
Matte, 383. 

Siphon-tap Essential in Smelting 
Green Fines, 283. 


Siphon-tap of Orford Furnace, 233. 
Size of Charge for Refining Furnace, 
345. 


Size of Ore for Reverberatory Smelt¬ 
ing, 322. 

Size of Smelting Charge for Cupolas, 
259. 


Size of Tuyeres, 257. 
Skimming-doors, Advantage of Two, 
330. 


Slag, Agglomeration of Fines with, 
280. 


Slag, Analysis of, from Blister Pro¬ 
cess, 338. 

Slag, Best Method of Handling, 288. 

Slag Brick, Manufacture of, 93. 

Slag Brick, Molds for, 94. 

Slag Brick, Weight and Size of, 95. 

Slag, Explosions of, 264. 

Slag from Clifton, Analysis of, 215. 

Slag from Copper Queen, Analysis 
of, 214. 

Slag from Reverberatories, Granula¬ 
tion of, 325. 

Slag, Granulation of, 288. 

Slag High in Silica, 283. 

Slag Suited to Blast-furnace Work, 
185. 


Slag, The Transportation of, 263. 

Slag, Use of, for Soaking Reverbera¬ 
tory Hearth, 308. 

Slag-cupola at Lake Superior, 216. 

Slag-cupola, Fore-hearth of, 219. 

Slag-dump, Importance of Keeping 
Level, 264. 

Slag-gutters for Reverberatory, 325. 

Slag-pots, 264. 

Slag-pots, Number Required, 264. 

Slags from Bessemerizing, Value of, 
for Flux, 383. 

Slating Arch of Calciners, 157. 

Slimes, Ore, Use of, for Lute, 321. 

Smelting, Cost of, in Herreshoff Fur¬ 
nace, 204. 

Smelting, Effect of Fines on, 261. 

Smelting for Coarse Metal, 319. 

Smelting for White Metal, 333. 

Smelting Green Fines, 282. 

Smelting Green Fines at Orford 
Works, 284. 

Smelting Green Fines, Thomson’s 
Method of, 283. 

Smelting in Blast-furnaces, 184. 

Smelting in Blast-furnaces, Remarks 
on, 256. 

Smelting in Cupolas, Cost of, 253. 

Smelting in Cupolas, Resume by 
Howe, 285. 

Smelting in Reverberatories, Im¬ 
provements in, 324. 







396 


INDEX. 


Smelting Nickel Matte, Salamanders 
from, 295. 

Smelting Nickel Matte, Use of Steep 
in, 295. 

Smelting Nickel Ores, Amount of 
Coke used in, 294. 

Smelting Nickel Ores, Use of Char¬ 
coal in, 294. 

Smelting of Copper, The, 181. 

Smelting, of Pyritous Nickel Ores, 
290. 

Smelting, Rapid, The Secret of, 
321. 

Smelting with Hot Blast, 258. 

Smelting-in of Reverberatory Hearth, 
308. 

Society of Chemical Industry, Gil¬ 
christ’s Paper before, 339. 

Sorting Ore during Hand-spalling, 54. 

Southern Carbonate Deposits, 18. 

Southern Carbonates, Production of, 
19. 

Sows, Freedom from, in Modern 
Smelting, 190. 

Speed of Rolls, 132. 

Spence Automatic Desulphurizer, 
141. 

Spence Furnace, Cost of Calcining in, 
143. 

Spence Furnace, Results Obtained 
from, 142. 

Sperry, F. L., Paper on Electrolytic 
Assay by, 39. 

Sperry on Battery Assay, Cuts of Ap¬ 
paratus, 41, 42, 43. 

Stacks at Detroit Refining Works, 
164. 

Stacks, Batter of, 161. 

Stacks, Construction of, 159. 

Stacks, Foundation for, 159. 

Stacks, Height of, 161. 

Stacks, Height of, for Reverberato- 
ries, 305. 

Stacks, Ironing of, 163. 

Stacks, Size of, 161. 

Stall-roasting, 92. 

Stall-roasting, Advantages of, 106. 

Stall-roasting, Cost of, 109. 

Stall-roasting, Cost of Stalls, 109. 

Stall-roasting in Open Stalls, 92. 

Stall-roasting of Matte, 115. 

Stall-roasting of Matte, The Manage¬ 
ment of, 115. 

Stall-roasting, Removal of As and Sb, 
104. 

Stall-roasting, Removal of Contents, 
104. 


Stalls, Amount of Wood Needed for, 

101 . 


Stalls at Parrot Works, 93. 

Stalls, Capacity of, 96. 

Stalls, Firing, 102. 

Stalls for Ore-roasting, 96. 

Stalls, Pearce’s Method of Covering, 

102 . 

Stalls, Size of, 99. 

Stalls, Size of Chimney Required for, 

100 . 

Stalls, Swelling of Contents of, 103. 

Stamps for Ore-crushing, 128. 

Steel Shells for Rolls. 130. 

Steep, Manufacture of, 193. 

Steep, Use of, in Smelting Nickel 
Matte, 295. 

Stetefeldt Furnace, 135. 

Stone Work in Reverberatory, Esti¬ 
mate of, 313. 

Strafford Furnace, Capacity of, 204. 

Stripping Roast-heaps, 78. 

Sturtevant Blower, The, 265. 

Sudbury, Addition of Green Fines to 
Smelting, 293. 

Sudbury, “ V-Method ” of Roasting 
at, 86. 

Sulphide Ores, The Treatment of, 
184. 

Sulphides, Oxidation of, in Banked 
Furnace, 247. 

Sulphur, Amount of, Present in Cal¬ 
cined Ore, 173. 

Sulphur Obtained in Heap-roasting, 
75. 

Sulphur Removed in Matte Stalls, 
117. 

Sulphuric Acid Made in Kilns, 118. 

Sulphuric Acid, Manufacture of, 
from Injurious Fumes, 59. 

Sulphurous Acid, Effect of, on Agri¬ 
culture, 57 . n 

Sulphurous Acid, Means for Obviating 
Effect of, 58. 

Summary of Totals for Reverberatory, 
316. 

Swansea, Home of Reverberatory, 
299. 


Swansea Method of Buying Ores, 183. 
Swansea Method of Copper Refining, 


343. 


Sweden, Refining Copper with Gas in, 
363. 

Swelling of Roasted Ore in Stalls, 
103. 


T 


Stall-roasting, Results of, 105. Tamarack Mine, Description of, 12. 

Stall-roasting, Time Required for ] Tap-hole, Difficulty of Opening, in 
Operation, 103. | Blister Furnace, 338. 



INDEX. 


397 


Tapping Reverberatories, 322. 

Tapping-ring, Improvements in, 286. 

Tetrakedrite, 5. 

Tetrakedrite, Argentiferous, 6. 

Thomson’s, J. L., Metkod of Intermit¬ 
tent Smelting, 243. 

Thomson’s, J. L., Metkod of Smelt¬ 
ing Green Fines, 283. 

Tie-rods for Calciners, 155. 

Time a Blast Furnace can Remain 
Banked, 245. 

Time Required for Blister Making, 
336. 

Time Required for Heap-roasting, 68. 

Time Required for Stall-roasting, 103. 

Titration witk Cyanide of Potash, 33. 

Tombstone Fine Ore Bricked witk 
Clay, 280. 

Torrance, J. Fraser, Use of Cement 
for Bricking Rick Fines, 278. 

Torrey & Eaton’s Investigations on 
Cyanide Assay, 36. 

Torrey & Eaton’s Investigations on 
Electrolytic Assay, 38. 

Totals, Resume of, for New, Large 
Reverberatory, 332. 

Totals, Summary of, in Building Re¬ 
verberatory, 316. 

Tracks for Roast Stalls, 112. 

Transportation of Slag, 263. 

Treatment of Fine Ore in Cupolas, 
275. 

Treatment, of Gold- and Silver-bear¬ 
ing Ores, 378. 

Treatment of Nickel Matte, 295. 

Trippel, Dr. A., Analysis of Melaco- 
nite, 2. 

Turning Roll Shells, 131. 

Turn-table for Roast-yard Track, 66. 

Tuyere-joint, Prof. Rickards’, 205. 

Tuyeres, Position of, in Mankes’ Con¬ 
verter, 381. 

Tuyeres, Proper Size of, 257. 

Tuyeres, The Size of, 209. 

Tuyeres, Water, for Brick Furnace, 
250. 

U 

United Verde Smelter, 209. 

Unroasted Matte, The Fusion of, 272. 

Use, The, of Basic-lined Furnaces, 
339. 

V 

Value of Converter Slags for Flux, 
The, 382. 

Varieties of Calcination, 46. 

Verde Mine, Arizona, 22. 

Vivian, Hon. H. H., Lecture by, 189. 

Vivian’s Dry-sweating of Copper, 354. 


Vivian & Co.’s Metkod of Fusing 
Nickel by Gas, 297. 

“V-Method” of Heap-roasting, The, 
87. 

W 

Walker River, Nevada, Mines, 20. 

Wall Accretions, The Removal of, 247. 

Water, Amount used for Copper 
Queen Furnace, 210. 

Water, Impure, Effect of, on Ingot 
Copper, 349. 

Water Tuyeres for Brick Furnaces, 
250. 

Water-jacket, 186. 

Water-jacket, Amount of Water 
Needed for, 188. 

Water-jacket at Copper Queen Mine, 
209. 

Water-jacket at Globe Mine, 209. 

Water-jacket at United Verde Mine, 
209. 

Water-jacket, Bartlett’s, Cut of, 225. 

Water-jacket by Fraser & Chalmers, 
Cut of, 224. 

Water-jacket, Fore-keartk or “Well” 
of, 189. 

Water-jacket, Form of, 187. 

Water-jacket, Height of, 206. 

Water-jacket, Herreslioff’s Latest, 195. 

Water-jacket, Life of, 222. 

Water-jacket, Table of Comparative 
Results 220. 

Water-jacket, Table of Results, 223. 

Water-jacket, Wind-box of, 205. 

Water-jackets, Free Circulation in, 
287. 

Water-jackets, The Management of, 

211 . 

Weight of Charge for Blister-making, 
335. 

Weight of Slag-brick, 95. 

Wendt, A. F., Losses at Ducktown 
from Leaching, 107. 

Wendt’s Description of Herreshoff’s 
Furnace, 200. 

Wharton’s, Joseph, Display of Metal¬ 
lic Nickel, 298. 

White Metal, Auriferous, Table of 
Results of Treatment of, 379. 

White Metal, Auriferous, The Treat¬ 
ment of, 379. 

White Metal, Smelting for, 333. 

White Metal, Treatment of, in Basic 
Hearth, 342. 

Width of Reverberatory Calciner, 146. 

i Wind-box for Water-jacket, 205. 

Wood Needed for Roast Stalls, 101. 

Wood, Use of, for Refining at Ore 
Knob, 345. 






398 


INDEX. 


Working-doors of Calciner, 149. 
Wrought-iron, Estimate of, for Build¬ 
ing Reverberatory, 315. 
Wrought-iron Fore-hearth, 287. 

Z 

Zinc, The Effect of, on Cyanide As¬ 
say, 34. 


Zinc, The Effect of, on Electrolytic 
Assay, 39. 

Zinc, The Precipitation of Copper 
with, 37. 

Zinc-blende, The Calcination of, 171. 
Ziervogel Method, 171. 

Ziervogel Method Suited only to Pe¬ 
culiar Conditions, 378. 


V 


1 













ADVERTISERS’ INDEX 


Abel’s Mining Accidents and their Prevention, - - - xvm 

Bridgeman, H. L., - . . - . . . . XXI 

Bullock, M. C., Manufacturing Co., - xv 

Chicago Iron Works, xvii 

Chism’s Mining Code of the Republic of Mexico, - - - vr 

Cowles’ Electric Smelting & Aluminum Co., ... m 

Endlich’s Manual of Qualitative Blow-Pipe Analysis, - - - n 

Engineering and Mining Journal, ..... 1V 

Fort Scott Foundry & Machine Works Co., .... XIII 

Fraser & Chalmers, ....... v 

Friedenstein, J., ....... XXI 

Harrington & King Perforating Co., .... xxvi 

Heil, Henry, Chemical Co., ------- X v 

Hendricks Bros., ........ XI 

Hoskins, W., --------- m 

Howe’s Metallurgy of Steel, ...... XV i 

Hunt's Chemical and Geological Essays, ..... xxn 

Hunt’s New Basis for Chemistry, ..... xxm 

Hunt’s Physiology and Physiography, ..... xxiv 

Hunt’s Systematic Mineralogy, ...... xxv 

Keyes, W. S., - -- -- -- -- xix 

Kunz’s Gems and Precious Stones of North America, - - xx 

Ledoux & Co., xix 

Lewisohn Bros., ........ IX 

Norwalk Iron Works Co., ... ... XXI 

Orford Copper Co., -------- vn 

Pennsylvania Salt Manufacturing Co., ----- xi 

Ricketts & Banks, - i 

Rothwell, Richard P., - ...... xix 

Scientific Publishing Co., ------- vm 

Stetefeldt’s Lixiviarion of Silver Ores, ..... x 

Wedding’s Basic Bessemer Process, ..... xn 

Wyatt’s Phosphates of America, ...... xiv 








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ADVERTISEMENTS. 


MANUAL 

OF 

QUALITATIVE BLOWPIPE ANALYSIS 

AND 

DETERMINATIVE MINERALOGY. 

BY 

F. M. ENDLICH, s. N. D., 

MINING ENGINEER AND METALLURGIST, 

LATE MINERALOGIST SMITHSONIVN INSTITUTION, AND UNITED STATES GEOLOGICAL 
AND GEOGRAPHICAL SURVEY OF THE TERRITORIES. 


Bound in Cloth. Illustrated.. Brie© Sl.OO. 


This work has been specially prepared for the use of all students in this 
grear, department of chemical science. The difficulties which beset begin¬ 
ners are borne in mind, and detailed information has been given concern¬ 
ing the various manipulations. All enumerations of species as far as pos¬ 
sible have been carried out in alphabetical order, and in the determinative 
tables more attention has been paid to the physical characteristics of 
substances under examination than has ever yet been done in a work of this 
kind. To a compilation of all the blowpipe reactions heretofore recognized 
as correct the author has added a number of new ones not previously pub¬ 
lished. The entire arrangement of the volume is an original one, and to the 
knowledge born of an extensive practical experience the author has added 
everything of value that could be gleaned from other sources. The book 
cannot fail to find aplace in the library or workshop of almost every student 
and scientist in America. 


TABLE OF CONTENTS. 

Chapter I.—Appliances and Reagents required for Qualitative Blowpipe Analysis. 
Chapter II.—Methods of Qualita tive Blowpipe Ai alysis. 

Chapter III.— fables giving Reactions for the Oxides of Earth and Minerals. 
Chapter IV.—Prominent Blowpipe Reactions for the Elements and their 
Principal Mineral Compounds. 

Chapter V.—Systematic Qualitative Determination of Compounds. 
Chapter VI.—Determinative Tables and their Application. 


THE SCIENTIFIC PUBLISHING COMPANY, 

PUBLISHERS, 


27 PARK: PLACE, NEW YORK. 








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Ill 


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ADVERTISEMENTS. 


The ENG1* E ™G 0BNA ^ 

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ROSSITER W. RAYMOND, Ph. D., M. E,, Special Contributor. 
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X 


ADVERTISEMENTS. 


The Lixiviation of Silver Ores 

WITH 

Hyposulphite Solutions. 

BY CARL A. STETEFELDT. 

Z - ' * 

In Cloth, Illustrated. Price, - - $5,00. 


Notices and Opinions. 

“ We can unreservedly recommend this work.”— Mexican Financier. 

Prof. Safford, of the Vanderbilt University, writes: “Mr. Stetefeldt has 
given us a most useful work and one well up with the times.” 

Prof. Comstock, of the University of Illinois, says : “There is a crying need 
of more works like it upon cognate subjects.” 

“ It is in every respect a model of what such a book should be and is another 
illustration of German thoroughness.”— Journal of Analytical Chemistry. 

Prof. Egleston, of the Columbia College School of Mines, writes : “ The 
book is a very valuable contribution to our knowledge of teaching, and I shall take 
great pleasure in recommending it to students, metallurgists and others.” 

“It is particularly valuable for its descriptions of the chemistry of the process, 
in which the older works are woefully deficient. It gives all the facts, apparently 
which one engaged in milling ore by the process should know.”— Mining Industry. 

Prof. HofmAN, of the Dakota School of Mines, writes : “I have no hesita¬ 
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XII 


ADVERTISEMENTS. 


BASIC BESSEMER PROCESS. 

By Dr. H. WEDDING. 


The Scientific Publishing Company has secured the rights 
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Professor of Chemistry and Metallurgy in the University 

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Late Engineer at the Basic Steel Works, Teplitz, Bohemia, and at 
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XIII 


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XIV 


ADVERTISEMENTS. 


THE PHOSPHATES OF AMERICA. 


Where M How They Occur; How They Are Mined; 

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XV 


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13 Y 


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Royal Quarto, Handsomely Bound, Printed on Superfine 

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SECOND EDITION. 

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XVII 


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XV III 


ADVERTISEMENTS. 



THEIR PREVENTION. 



BY SIR FREDERICK AUGUSTUS ABEL. 


With Discussion by Leading Experts. Also, the United 
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the Working of Coal Mines. 

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Contents: 

Mining Accidents. By Sir Frederick A. Abel. With discussion by President 
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ADVERTISEMENTS. 


XIX 


W. «. KEYES, 

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XX 


ADVERTISEMENTS. 


THE UNANIMOUS OPINION 

OF THE BEST CRITICAL JUDGMENT OF THE WORLD IS THAT 

THIS WORK IS THE 

MASTERPIECE OF LITERARY, ARTISTIC AND TYPOGRAPHICAL ART. 



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XXI 


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XXII 


ADVERTISEMENTS. 



ESSAYS 


BY- 


THOMAS STERRY HUNT, 

Author of “ Mineral Physiology and Physiography,” “A New Basis 
for Chemistry,” “Systematic Mineralogy,” etc. 


FOURTH EDITION. JUST PUBLISHED. WITH NEW PREFACE. 


PRICE, $2.50. 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

Till. 

IX. 

X. 

XI. 


TABLE OF CONTENTS. 


Preface; 

Theory of Igneous Rocks and Vol 
canoes; 

Some Points in Chemical Geology; 

The Chemistry of Metamorphic 
Rocks; 

The Chemistry of the Primeval 
Earth; 

The Origin of Mountains; 

The Probable Seat of Vocanic 
Action; 

On Some Points in Dynamical 
Geology; 

On Limestone, Dolomites and 
Gypsums; 

The Chemistry of Natural Waters; 

Petroleum, Asphalt, Pyroschists 
and Coal; 

Granites and Granitic Vein¬ 
stones ; 


XII. The Origin of Metalliferous De¬ 
posits; 

XIII. The Geognosy of the Appala¬ 

chians and the Origin of Crys¬ 
talline Rocks; 

XIV. The Geology of the Alps; 

XV. History of the Names Cambrian 
and Silurian in Geology; 

XVI. Theory of Chemical Changes and 
Equivalent Volumes; 

XVII. The Constitution and Equiva¬ 
lent Volume of Mineral 
Species; 

XVIII. Thoughts on Solution and the 
Chemical Process; 

XIX. On the Objects and Method of 
Mineralogy; 

XX. The Theory of Types in Chem¬ 
istry. 

Appendix and Index. 


THE SCIENTIFIC PUBLISHING COMPANY, 

PUBLISHERS, 

27 PARK PLACE, NEW YORK. 


















ADVERTISEMENTS. 


XXIII 




A CHEMICAL PHILOSOPHY 


BY 


THOMAS STERRY HUNT, m.a., ll. d., 


Author of “Chemical and Geological Essays,” “ Mineral Physiology 
and Physiography,” “ Systematic Mineralogy,” etc. 


THIRD EDITION, REVISED AND AUGMENTED, WITH NEW PREFACE. 


PRICE, $2.00. 


of 

I. Introduction. 

II. Nature of the Chemical Process. 

III. Genesis of the Chemical Ele 
ments. 

IV Gases. Liquids and Solids. 

V. The Law of Numbtis. 

VI. Equivalent Weights. 

VII. Hardness ana Chemi¬ 
cal Indifference. 


CONTENTS. 

VIII. The Atomic Hypothesis. 

IX. The Law of Volumes. 

X. Metamorphosis in Chemistry. 
XI. The Law of Densities. 

XII. Historical Retrospect. 
XIII. Conclusions. 

XIV. Supplement. 
Appendix and Index. 


THE SCIENTIFIC PUBLISHING COMPANY, 

PUBLISHERS, 

27 PARK PLACE, NEW YORK. 



















XXIV 


ADVERTISEMENTS. 


MINERAL 


PHISKWY AND 



I 


A SECOND SERIES OF 

CHEMICAL AND GEOLOGICAL ESSAYS, 

WITH 

A GENERAL INTRODUCTION. 


BY 


THOMAS STERRY HUNT, m. a., ll. d., 

Author of “Chemical and Geological Essays,” “A New Basis for 
Chemistry,” “Systematic Mineralogy,” etc. 


SECOND EDITION. WITH A NEW PREFACE. 

PRICE, $5.00. 


TABLE OF CONTENTS. 

Preface. 

Chapter I —Nature in Thought and Language. 

Chapter II.—The Order of the Natural Sciences. 

Chapter III.—Chemical and Geological Relations of the Atmosphere. 
Chapter IV.—Celestial Chemistry from the Time of Newton. 

Chapter V.—The Origin of Crystalline Rocks. 

Chapter VI —The Genetic History of Crystalline Rocks. 
Chapter VII.—The Decay of Crystalline Rocks. 

Chapter VIII.—A Natural System in Mineralogy, with a Classification of Silicates. 
Chapter IX.—History of Pre-Cambrian Rocks. 

Chapter X.—The Geological History of Serpentine, with Studies of Pre- 
Cambrian Rocks. 

Chapter XI.—The Taconic Question in Geology. 

Appendix and Index. 


THE SCIENTIFIC PUBLISHING COMPANY, 

PUBLISHERS, 

27 PARK PLACE, NEW YORK. 


















ADVERTISEMENTS. 


XXV 


SYSTEMATIC MINERALOGY 

BASED ON A 

NATURAL CLASSIFICATION. 

WITH A GENERAL INTRODUCTION. 


THOMAS STERRY HUNT, m.a., ll.d„ 

Author of “ Chemical and Geological Es-ays,” “Mineral Physiology and 
Physiography,” “A New Basis for Chemistry,” etc. 


BOUND IN CLOTH. PRICE $5.00. 


The aim of the author in the present treatise has been to reconcile the 
rival and hitherto opposed Chemical and Natural History methods in Min¬ 
eralogy, and to constitute a new system of classification, which is “ at the 
same time Chemical and Natural Historical;” or, in the words of the preface, 
“ to observe a strict conformity to chemical principles, and at the same time 
to retain all that is valuable in the Natural History method ; the two 
opposing schools being reconciled by showing that when rightly under¬ 
stood, chemical and physical characters are reall y dependent on each other, 
and present two aspects of the same problem which can never be solved but 
by the consideration of both.” He has, moreover, devised and adopted a 
Latin nomenclature and arranged the mineral kingdom in classes, orders, 
genera and species, the designations of the latter being binomial. 


TABLE OF CONTENTS. 


Chapter I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 


IX. 


The Relations of Mineralogy; 

Mmeralogical Systems; 

First Principles in Chemis' 
try; 

Chemical Elements and No - 
tation; 

Specific Gravity; 

The Coefficient of Minera 
Condensation; 

The Theory of Solution; 

Relations of Condensation to 
Hard ness and in a nlubility; 

Crystallization and its Rela¬ 
tions ; 


Chapter X. The Constitution of Mineral 
Species; 

XI. A New Mineralogical Classi¬ 
fication ; 

XII. Mineralogical Nomencla 
tare; 

XIII. Synopsis of Mineral Species; 

XIV. The Metallaceous Class; 
XV. The Halidaceous Class. 

XVI. The Oxydaceous Class; 
XVII. The Pyricaustaceous Class; 
XVIII. Mineral History of Waters; 
General Index; 

Index of Names of Minerals. 


THE SCIENTIFIC PUBLISHING COMPANY, 

PTJBLISHEKS, 

27 PARK PLACE, NEW YORK. 










XXVI 


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